1sweed, I had a similar problem with my ex and him not believing my pain.
When my fibro started I was with my (now) ex. He saw my condition literally suck the life out of me gradually for over two years. During this time I had not been diagnosed, and we didn't know why I had all these worsening problems. He had a very difficult time sympathizing (or believing) with my pain and it changed the entire dynamic of our once loving relationship. He got frustrated with me since I just would not get better, and our intimate life suffered since he just saw me as a "sick person". He grew to resent me, saying "its all in my head" when blood tests were negative, he called me lazy when my fatigue was bad, and when we fought he would say in anger that he didn't want to be with someone who was going to end up in a wheelchair at this rate. Needless to say we didn't work out!
I'm with someone else now and I was diagnosed a few months into our relationship. Since then he is always asking me how I slept or how I am feeling today which I think is really sweet. However, I think he has a hard time hearing about my pain, and he usually cuts me off to tell me everything will be ok. He even tells me that I'm beautiful when I break out in rashes.
I know I'm lucky now, but a part of me is still fractured from the painful things my ex put me through. I just hope my current boyfriend can stay as supportive as he's been, and doesn't start to resent me.