How to change for the better and preserve your relationship

At this point, I loathe myself. Truly hate who I've become as a person and am purely disgusted with myself. Each day I wake up and I think about what I done. How could I do it again?! I've hurt him more than once and he has been nothing but faithful to me. Two years into a relationship and I ******* ruined it! The guilt ate me alive so I came clean to him and I'll never be able to shake the image of his face when I told him and his crying. No matter how drunk I get, no matter how good a day it is I can't shake it. I know it's my fault. I know it's low down and heart wrenching. I know what pos I am for it. I won't deny any of that. I just got so beyond angry and felt like for some reason maybe he was sick of me and instead of ending it I cheated. I didn't go all the way but still a sexual act was performed. I had no feelings at all during it either. Not happy, not excited, not mad, not sad. Literally not a single thought. Almost like I couldn't think. Afterwards, however, I felt awful. So awful I attempted suicide only for him to save me from myself. Had he not gotten home when he did, I probably wouldn't be alive today. I know it's selfish but I couldn't cope with what I had done. I'm still battling it every moment I'm a wake, even having nightmares from it which I know I deserve. I understand that I deserve every bad night of sleep, every horrible moment. He is working on forgiving me, if I were him I don't know that I would do the same. He is trying to move forward and that's what I want. I'll do anything to make it work. I've even scheduled a counseling session, given up all passwords to anything I had, everything. I will right this one way or the other because he deserves so much better and he wants it to be me so I will change anything and everything even if that takes therapy. My question is how do I even begin to forgive myself? How do you when you hate it and don't even know why you did it?