don't know what to do anymore...

So myself and my partner when we was first together I went through a very difficult time. And no that isn't an excuse... I had got to a point with my depression that I felt like I wasn't good enough or wanted by anyone... so the first bloke that showed me attention I slept with... he was disgusting and I mean gross!!!! I would have never ever gone there if I want ill. Makes me feel sick thinking about it! The first thing I done was phone my other half and tell him. He didn't want me to leave him he wanted me to stay.. 8 months in and he rings me daily talking about it telling me he hates how he looks because of how skanky the other one was.. but I hate myself every day for doing it. It's got to a point I hate myself so much for doing it to him I'm hurting myself regularly to feel some kind of punishment for what I have done. What do I do? How do I get out of this ruck?! 😓