I'm scared that if I fall, I'll have to start over again and it's gonna be hard. I've come so far and I dunno if I'll start again...
I think it's important that you realize the koach and importance of each and every second clean. Each individual second will stand as a defense and s'char for you at 120 Iy"H. As important as counting 90 days may feel, never lose sight of the REAL goal: Total abstinence ONE DAY AT A TIME.
Even if you fall ch'v, it would not mean you were back to square one. All it would mean is that you lost a few seconds, and were continuing the climb from almost the place you left off.
Rabbi Akiva remained away from home 24 years straight, even though he was right next to his front door after 12 years. Why didn't he at least stop in, say hello to his wife and then return? Because 12+12 is not the same at 24 straight without interruption. BUT, even if he had come home, that would NOT have negated the first 12 at all.
So too with this addiction. You say you wouldn't have the strength / desire to start again if you fall. So I'm telling you, 'not true'. Its not 'all or nothing'. HKBH wants to see effort, and each and every second clean is a precious gem in His crown. Keep adding those jewels!