Sadly, I'm going through a similar situation. I was dating a girl and we were amazing together. We had so much fun and clicked. I loved her deeply, she loved me deeply. My drinking and explosive temper while drunk, made her re-evaluate those feelings for me, and she didn't love me anymore.
We tried to be friends, basically me showing her I can stop drinking, and be a better person, and I was successful for a couple of weeks. She wasn't able to find those feelings again for me.
I am plagued with so much guilt, and shame, and embarrassment, and especially regret.
It's these feelings that ultimately brought me here, and brought me to making sobriety a priority. It's been really damn hard, and I wish I could say I've been successful, but I'm back to Day 2 today, and I cut her out of my life completely now so I can move on.
I've learned a lot about myself and my future with drinking. I know I can't "just have a few" or control my drinking. It has to be gone if I ever want a family. So I'm trying, and struggling.
I'm sorry for where you are at now. You can't take any of it back, but an apology will of course mean a lot. If the relationship is over, learn from it, and make changes, so it doesn't happen again.
I'm certainly trying.
Good luck.