Undoubtedly, going to the מקוה brings טהרה. Undoubtedly the OP feels cleansed after he immerses. Whether that feeling is perceived, or it's based on the purity that's actually happening, is not my place to say. I would imagine that there are some people in our generation that can tap in to those sublime realities, but for most regular people, I would think that the awareness that טהרה is taking place, fuels a feeling of purity that people convince themselves of feeling. But all that IMHO is not the point. If I understand correctly, there's a deeper question that's being asked.
When someone is in an active struggle, often what can happen is, they find ways to cleanse themselves of the guilt that comes along with the sin, and use it to enable them to sin. It takes a lot of soul searching, and real introspection to figure out if the reason you fall right after going to the מקוה isn't precisely because of the the feeling that "I can easily just dip, and viola - feel clean again". Obviously this isn't done on a conscious level. But if a person knows that there's a way out of the yucky accompanying feelings, then subconsciously he won't work as hard to restrain himself before the fact.
To me there's no question, that if by going to the מקוה he'll sin 20 times a year, and by not going to the מקוה, he'll sin fewer times, there's no question that the טהרה he attains by not sinning is far greater then any טהרה he'll achieve by going to the מקוה and immersing himself ש"י טבילות.
Again, this is not ח"ו a knock on going to the מקוה, it's merely pointing out, that if a person, at any point finds, that he's using the מקוה as a quick fix, then he might better off not going. It smacks of אחטא ואשוב, where one utilizes תשובה to enable him to sin. The greatest טהרה he can immerse himself in, is refraining from sin.
If he finds that this is not the case, that everything I just wrote wouldn't be relevant, and he should continue going.
