We have a new valiant warrior on the forum who goes by the alias "Ykv_schwartz". He recently wrote a very enlightening post to someone who had been clean for 90 days and then had a fall (edited a bit for clarity):
There are some fundamental points that post-addicts must realize. I myself have gone six months completely clean with very few test along the way, and after that I fell. I have learned from my own mistakes what needs to be in place after "escaping" the claws of the Yetzer Hara.
1) Firstly, the fact that you were able to fall back to it so quickly is a sign that your brain is not rewired yet. I read that it can take up to three years to rewire one's brain. I have learned this lesson the hard way. My ultimate down-fall came in a very similar experience as yours, where I had access to open internet suddenly one day and the curiosity got the better of me, and I was gone. It was then that I realized that my brain has not really been rewired, some of the associations had been suppressed all those months, but they had not been erased. So the first issue to understand is, that just because one thinks he is cured, he is not. We should realize and understand this.
2) The second issue is related to the first, and that is, that the life of a baal teshuvah is different than the life beforehand. A few weeks ago, I was invited to a neighbor's get-together for the birth of their daughter. These neighbors of mine have a different level of observance than mine and their event was co-ed. I walked in to say mazel tov and I saw men and women intermingled throughout this house. Besides the fact that I was mortified by the sight, I realized that this is not a place for me. It wasn't that I felt aroused by being there (B"H, I have greatly worked on myself in this area over the past few years), but I felt it was not even appropriate for me to enter just to say mazel tov. So even though this neighbor of mine may get insulted or whatever, those are the sacrifices we have to make in life. So we need to be extremely careful what we do, where we go, etc. As a policy, I do not go to certain places. I even stay away from shopping centers if possible. To what extreme a person decides to take this upon himself is personal. But the point is, that a baal teshuva has to make changes to his life. He cannot think that life is back to normal again. This is a fundamental mistake I made. I felt "cured" and my guard was down, and before I knew it, it slowly made its way back into me.
3) Third point: We need to not only make physical changes to our lives, but perhaps more importantly, we need to strive for heightened levels of kedusha. As many on this forum pointed out, "sur-me'ra - turn away from bad" is not enough on its own, you also need "aseh tov - do good". This means to begin building one's kedusha all around. It starts by controlling one's body, which means not only controlling the movement of our hands - which by now, for some, has become second nature. But it also means working on stopping to intentionally allow erections to occur, and it means knowing how to react when that happens accidentally. One must realize there are prohibitions involved. Then one can work on not dwelling on fantasies, purifying one's mind, and it keeps going. The point is, to grow spiritually in general and in kedusha specifically. Again, this is personalized. One person may feel he wants to work on reducing his focus on gashmiyus in general. Everyone is different, but the principle is the same. It really all boils down to what someone posted recently, "what do I want out of life? To be a prisoner of my body or a servant of Hashem?". Truly accomplishing this, comes not only through the power of 'refraining', but also through the power of positive growth.
4) The fourth and final point I would like to make here, is a less well-known yetzer hara called "the yetzer hara of milestones". There is a catch-22 that many of us here on the forum are faced with. We all encourage ourselves to strive for the top of the ladder of 90 days. This is great, as it helps us stayed focus. But when a person hits a milestone in life, there is little voice telling him, 'you did it! great! You are the best! Now you could go back and do a little of that bad stuff again'. We must realize that milestones in life are not the end, but rather a beginning. When a person falls from his milestone (as I did), he did not mess up the past. But the yetzer hara of milestone makes us look at the past, not at the future. We hit a point and look back at our accomplishments and forget the future ahead of us. We forget that the milestone's only purpose was to prepare us properly for the future.