Chronic Pain and Sex

So I have a ton of medical issues that cause me to be in constant pain. I have degenerative disc disease, post laminectomy syndrome, fibromyalgia, and chronic fatigue syndrome (along with other diagnoses that I'm probably forgetting). On top of that I have bipolar disorder as well and I have a really hard time getting in the mood due to the mental and physical issues. There are days when I can't even stand to be touched due to pain and I often feel incredibly guilty because I want to be intimate with my boyfriend. We have been together for 7 years next month and I will say that he is incredibly understanding and patient with me. How do you get through the guilt and be intimate with the man I love? It really sucks especially when I do finally feel good enough to have sex but then end up hurting halfway through.