Masturbation leading to clouded judgement

Like most people on here, masturbation has plagued me for a long time.

Recently, I got into a serious relationship with a girl who I think I love very much, but she's always been very insecure about my sexual history. I had a period when I would get real horny, go out and do something stupid, finish, and then feel shit. I'd often end up hurting myself. It's like when I'm aroused I go into some sort of alter state, and when I come out of it, it's like I wake up. A few days ago I gave into one of these moments of weakness and I cheated on her.

How do I stop testosterone from controlling my life?