<human>: Can you succinctly summarize the text in 1-3 sentences?

I did something horrible and don't know what to do. My gf of 8 years cheated on me years ago and we made up everything had been great. Now I cheated and can't bring myself to tell her. I'm literally sick to my stomach since it happened. I know it's not an excuse but I was drunk and I don't even know why I did it. It's even worse b/c it was a good friend of ours that I've been friends with for a long time. We have agreements in place for a semi open relationship but no sex and I know it. I remember how awful I felt when she told me years ago. I was hurt for so long. I just can't bring myself to tell her. If it helps I'm 27 she is in her 30's. We have been together for 8 years and are both women. I cheated with a friend and I hate myself.
<bot>: cheated on my wonderful woman with a close friend can't bring myself to tell her b/c I can't hurt her. WTF is wrong with me?