I think deep down, you seek discipline. You've talked about stopping drug use, and you admit that these flings with women you don't truly care about are losing value, that tells me that you are seeking self discipline. You're growing up
But not only do you seek greater self discipline, and a stronger resolve within... you also wish to be held accountable by those around you. This is the feeling you are getting from Sara, because although she is not a perfect match for you compatibility wise, the one thing she does do, is hold you accountable
She doesn't reward your bad behavior, she punishes it, in her own crazy way. This is the complete opposite of most of the women you deal with. The other women you described, constantly reward your bad behavior. Case in point being the woman who is still rewarding you, even after you lied to her about that STD