I am 20 years old (not too old) and I have been struggling with this addiction for close to 7 years.
It sounds like you:
a) realize you have an addiction
b) have been trying to stop for a considerable amount of time
c) have proven to yourself that you can't do it on your own
This was my pre-marriage story with the exception of item a).
Stopping for 90, 190 or 290 days is not really the issue.
In my experience I was sober at times for over a year and eventually went back to my behaviors with the difference that I then added some new ones.
I have found that what I need is
recovery. That is very different from just stopping doing certain behaviors.
If I had a dollar for every time I heard an addict say "I thought that marriage would help / solve / improve my addictive behaviors, but it didn't" I wouldn't be a millionaire but I could go out for a really nice dinner
The nature of my addiction is that it is the "answer" to all my problems. It makes me numb to the pain, anger, frustration, resentment and other bad feelings.
As an addict I have a whole host of character defects that not only don't go away in marriage but get aggravated, aroused and break open in full fury. And guess what my brain tells me the solution is? Yep. LUST.
So for many of us, Marriage -> greater stress -> greater need for relief -> greater need for LUST.
I don't mean to rain on anyones parade but age 20? You have hopefully a very long life lying ahead. You have the blessing from Hashem to realize you have issues to address that many of us never realized or were willing to face. If you take this opportunity to really find a solution, not just stop for a bunch of days, you will probably have an AWESOME life!!!!
Whatever road you take in the end your in the good hands of HASHEM so just focus on doing what is right.