Cheated on my girlfriend once.

Protection was successfully used and everything. I managed to avoid sex for a month with her afterwards so I could test for STDs anyway. Came up clean.

Plan was if I came up positive for anything, I'd tell her what happened. If clean, I'd just move on. So I haven't told her and I still don't plan to.

It's a cop out to not tell her, I fully know that, but I rationalize it that the deed has been done, I can't take it back, I'm clean so there is no risk to her. And telling her would only her, and would hurt me even further.

Seriously though, don't cheat on your partner, if you have any kind of conscience it's just such a horrible slimy feeling. I would feel terrible about it all day for a good while afterwards and it would really drain me. I couldn't even look at myself with any sort of self-respect for a while. The way I moved past it was to basically just mentally leave my former self in the past and tell myself that I'm no longer that person and I'm an entirely new me since doing that. For the most part I really am past it, but once in a while I'll get a nagging, remorseful thought about it still.

I love my girlfriend so much and have no idea why I would do something so awful to her. All I can do is tell myself I've learned from it and to never ever make that mistake again.