Hey,
Mazel Tov
From one engaged guy to another, I can definitely relate to engagement being a difficult time.
I want to be clear that I am not saying what I am about to say as judgmental at all. What you are experiencing with regards to looking at other women is 100% because of the false projections of marriage and love in western society. You already are working on so many things in life which is evident of you being here on GYE and that is already extremely impressive, but one thing that we as men of western society need to do is to change our perspective. There is one thing to know whats wrong and twisted and another to really internalize it and change our perspective to a healthy one.
226 days is extremely impressive and shows that you have extreme strength and commitment to staying clean. Since I don't know where you are at with regards to your mindset, which is a different part of this challenge and is crucial for long term maintenance, I will try to explain everything that I have learnt with regards to my perspective of women and marriage. I am sorry if I say anything that you already know but it will be helpful for people that read this that don't know it.
There are a few main topics I will try to discuss, objectifying women, Lust in marriage, sex in marriage, intimacy and love, and struggles of engagement. Again, I am going to write about these but I am not writing obvious things with the assumption that you don't already know them, rather with the assumption that someone else that does not know will be reading. What I am about to write is the perspective I have developed over the past 500+ days by talking to and interacting with some amazing mentors on this site.
One of the first parts of changing our mindsets for long term success in fighting the yetzer hara is to de-objectify women. The porn industry and western society as a whole has become extremely provocative and promotes the objectification of people and especially women. As you mentioned this is completely false and we need to rewire our brains to think of women as people rather than objects of pleasure. Women have emotions and lives which we need to treat with respect as a fellow human being. This is where shmiras eynayim comes in to play.
Shmiras eynayim is about respecting women, jewish and non-jewish, regardless if they are tznius or not. We need to respect them so that we can have true self-respect and to have the ability to respect our wives (and future daughters BezH). When we look initially out of instinct then that is not in our control and we must make sure not to linger, fantasize, or look back because that is when it crosses the line from instinct to animalistic Lust, which rips away their humanity and turns them into a object of lust for our own twisted pleasure. We cant truly respect ourselves if we don't respect others and we need that self respect in order to live lives of shalom. This is also why looking at billboards and other advertisements because in doing so we disrespect ourselves by lowering ourselves to look.
We cant control how they look, we can only control how we react.
Due to our exposure to porn and western cultures perspective of sex and marriage we have an unrealistic idea of what marriage will be like. Many bachurim and chassanim have the idea of their marriage being full of sex and fulfilment of their desires, and this is really detrimental to a marriage. When marriage and especially sex in marriage is solely about the physical, then the relationship gets lost. When a person uses his wife as a way to just satiate his desire, he is corrupting the true beauty of marriage and replacing it with Lust. This is where people go wrong when they think that marriage will help cure their desire. Marriage only helps with taivah when sex and intimacy in general is done in a proper way with a healthy mindset.
When we are deep in Lust, especially when we use our wives to try and fill that desire, we distance ourselves from others emotionally. We tend to use Lust as a way to numb our emotions that are difficult to deal with, like stress, anxiety, depression.... and we block or never even develop the tools to deal with these emotions in a healthy way. What ends up happening is that these numbed emotions end up resurfacing and compound with new difficult emotions, and we keep trying to numb them over and over. We then become callous without even realizing and we tend to unintentionally and sometimes intentionally, out of anxiety or fear, block out true connection in any of our relationships due to the overwhelming emotions that come with them.
This distance that is created, whether intentionally or not, is detrimental to a healthy marriage. We all know that women tend to be more emotionally in tune than men. Well this is true with regards to sex in marriage as well. Women need that intimate and emotional connection more than the physical. A wife will instinctually know when a husband is just using her and not connecting with her on that emotional level, and she may start to feel abandoned and not valued by her husband because he wont connect with her intimately. Meanwhile the husband may be oblivious to this because he is numb from lust and has these views from western culture.
Lust kills Love, Love = Intimacy, Lust kills Intimacy
What is intimacy? Unfortunately most people believe that intimacy is just sex. In reality sex is only one aspect of intimacy. Intimacy is what takes place in the day to day interactions of your relationship with your wife which add to the feeling of true love.
Love is not just an emotion. The initial stages of a relationship are full of this emotion that people feel as love. While there is a spark of love there and there is the start of a relationship, this love is really infatuation. True love is a choice. Love is something that is intentional and needs constant work. True love is creating an environment of safety and intimacy that you and your wife can connect with each other. During engagement is the start of the building of that true intimate relationship.
The main types of intimacy are emotional, recreational, physical, and sexual (there are more but I am forgetting them at the moment). Intimacy is how a husband and wife truly connect on the deepest of levels, and that connection is what develops a deep love for each other.
Emotional intimacy is, in my opinion, one of the most important and foundational parts of a marriage. The ability to trust, feel comfortable, respected, cherished, and valued is crucial for a marriage. This form of intimacy is also usually the form that is most valuable to women. Women need that feeling of trust and comfortability in order to feel loved and cherished.
Recreational intimacy is doing activities with your wife and getting to see different sides of her personality in different situations and vis versa with her getting to know you. This is mainly focused on during dating but is also crucial to have during marriage and usually gets lost with the advent of a busy life. It is still very important to continue going on dates once married even if you may not have time. The investment into your relationship will make the rest of your life better as a whole.
Physical intimacy is not sex and does not have to be sexual. For a woman, especially one that is shomer, it is a very special and intimate thing to trust her husband with this. A hug, a kiss of affection, even a holding of hands is something that enhances your relationship with that special connection and that trust she gives her husband should be cherished. To be held and feel secure, to hold a hand and just know that your not alone.... and many more than I can imagine. (we'll get to the hardships of fantasy during engagement)
Sexual intimacy is the culmination of your love and emotions for each other and is one of the holiest things in judaism. When a husband and wife connect in this way they bring the schina into the home. I could go into more depth but I don't think that I can post that on the singles forum and I don't have access to the bal habatim forum

.
There is also I believe financial intimacy as well and maybe a few more that I am forgetting.
Again, engagement is extremely difficult. When dating there is this amazing bubble of just you and your now kallah going on dates and having a good time with each other. Now during dating there is really a step back from each other even though your relationship has gone to the next level. Especially for us as guys where we don't need to do much but choose a tallis bag and show up to the wedding in our suit.
A very difficult part which I think you can relate with is the fantasising. We are in this weird stage where she is still not mutar to even think about in this way but our mind and our bodies are closer to having this deep, emotional, and intimate connection become even greater with, a muttar, sexually. Something we need to try to internalize and change is our desire for her.
We need to change our desire "for her" to instead a desire "to be for her". Fantasizing about her is really us satiating our desire with disregard to how she is and who she is. If we change our perspective to truly want to love her and be with her then we need to control ourselves to be with her and at her level of the relationship.
To add to that, just like she is not mutar now to think about and look at in that way, so to when she is a Niddah and we need to practice on making sure that we value her for more than just the physical part of the relationship. We need to value her from her perspective of how she feels valued rather than our warped view on how we think women feel value.
I hope that I made sense and if you feel like this is too much for your thread then I can take it down and move it to mine.
If you want to talk more message me!
Again, Mazel Tov!!
Keep on Trucking, One Day At A Time!!