As a male with Fibromyalgia, I will try and give you some advice. You complain about your boyfriend not being understanding, but that is a little hypocritical, as you seem to have a complete lack of understanding of his needs.
You are not alone, because most women have a complete lack of understanding of a males sexual needs, and how those needs are essential to a mans biological and emotional well-being. I will explain this more later...
What you need to do is sit down with him, and explain to him that you have been inconsiderate of his sexual needs. Once you admit to that, you can discuss how he has been inconsiderate. Tell him that you understand his needs, and you are going to do much better to meet those needs.
Then you tell him that if you guys are going to make your relationship work, it is going to take effort from both sides to be understanding. Tell him that if he is willing to do his part, and try to understand this disease, and how it affects your life, then you will do your part to save your relationship. It is going to be hard on both of you, and it is going to take a lot of effort from both parties.
A males sexual needs are very complex, and very different from a women. Men get "horny" in a very different way. It is not easy to explain, or understand unless you have felt it for yourself. A mans sexual desire is driven by two things... Emotional need, and biological need.
First I will try and explain the biological need, which is much different from a women. The biological need is driven by hormones. These hormones cause intense urges, that will not go away.
The closest thing to compare it to, is hunger. When you are hungry the brain is getting signals to tell your body to eat. These signals will not stop until you eat. It is a survival mechanism that is built into your DNA.
Now imagine if your brain was receiving signals 100 times as strong as hunger, and food was sitting right next to you and you couldn't have it. These signals for sex are caused by hormones, and they can be so powerful that a man can not sleep, or function until these signals are stopped.
For a women these signals pass, but for a man they just grow stronger and stronger until his biological need for survival is met. A man has very little to no control over this, and it will continue until he has had sex or masturbated.
Masturbation is not a solution, because a mans needs are far more complex than just the biological drive. Now you have to consider the emotional aspects.
Men are very insecure. They constantly have to feel needed, WANTED, and loved. You can communicate this with words, but men are physical, and visual beings. Sex is actually a form of communication for a man. when you open yourself up to him, you are telling him "I want you, I accept you, I love you, you are a part of me." Refusing to make love to a man causes intense feelings of rejection. By doing that you are subconsciously telling him "I do not accept you, you are not important to me, you are not a part of me, you are not wanted, I don't love you". Of course that isn't true, but those are the feelings that your act of rejection cause.
That is the best I can describe a mans sexual and emotional needs, even though they are much more complicated than that. You need to meet those needs, if you want your relationship to work. If you don't meet his needs sexually, your relationship will fail. Take initiative, take the first step, if you want to save your relationship. Sitting around blaming each other will never solve your problems. You have to solve these problems together, it doesn't matter whose fault they are.
Sex is an enjoyable thing, it usually doesn't hurt:-) You may need to have sex with him when you don't feel like it. Once you get into it, I am sure you will enjoy it. Since you don't have that strong biological drive that all men have, you may need to find things that help get you in the mood, have "quickies", or try positions where you don't have to do a lot of work. It won't take much to satisfy him. It doesn't have to be great every time, just as long as he feels wanted and accepted.
Now back to your needs. Once you are meeting his needs, you need to communicate exactly what your needs are. Spell it out for him. Don't assume anything. If something is very important to you, make it very clear how important it is to you. Lack of communication is the number one cause of failed relationships. Nine times out of ten a man will do anything for his women, as long as he knows what to do, but too many times people don't talk about what their needs are, and the relationship fails.
If he does not meet your needs after you are meeting his, and you have made your needs clear, then you should probably move on. There are a lot of nice guys out there! But they are all going to have sexual needs, so you are going to have to do something to address this problem.