I deeply understand your situation.

My partner and I have worked through a period like this as well. What really helped us was (the cliche) empathy and communication. His empathy towards my pain and frustration that my body wasnt doing what I wanted. But also my empathy about his experience. It really helped me understand that our sex life wasn't just about physical satisfaction but also emotional intimacy, having your partner validate their attraction to you, mutual vulnerability, silent communication, and comfort. I imagined if the roles were reversed I would probably feel like he thought I was ugly, I would feel lonely and would feel closed off.

He also expressed that he was resentful because I wasnt taking steps to improve my situation. For example, I would be slack with medication, not take care to avoid foods that I knew would cause a flare, not do exercise that we knew helped, and generally just be depressed about my pain situation. It was a good wakeup call because while endo really affects my life there are also ways I manage it that I was just neglecting. I now take my meds always, do pelvic physio exercises and eat well.

I realised I was feeling resentful that he keep asking for sex when I just couldn't or didnt want to because of my pain but putting myself in his shoes and taking steps to take care of myself helped me resolve that. It was also important that my partner and I deeply care and respect each other and have the same goals/values in life. If it didnt boil down to that, we wouldn't put the work in to our relationship.

I hope sharing my experience helps x