I wasn’t very nice to my ex girlf when we dated.

I did cheat on her amongst other things, mainly belittling her in front of our friends. I do feel bad about it now, but the way she laughs about the things that have happened to me (getting caught bullying, wetting myself when I was drunk, having no friends) really hurts.
It was a long time ago and I’m a really different person now, I’d like to be friends with her, but she’s being really horrid.
I have apologised but apparently it’s not enough.