Sorry you are feeling like this, Erin. I hope things start to improve soon for you... well as much as they can MS wise.
I've been ill since I was 12 years old and even before that dealt with my grandmother who had MS so I understand what you are going through. I KNOW how horrible it is to be ill at a young age, to not have people understand etc and the "friends" thing I definitely understand.
Because I became ill during my school years, it meant that all of my friends walked away from me. They didn't like the fact that I was in a wheelchair (hey, neither did I

) and they wouldn't make the effort to come over to see me (I was home schooled after a while due to mobility issues, horrible comments etc). It was awful and I was all alone, except for my parents. Even now, they still don't talk to me. I haven't heard from any of them in about 6 years.
I slowly started to realise that it wasn't MY fault they didn't stop around... I couldn't help being ill. I tried everything on my part to make them stay, inboxing them on Facebook etc. NOTHING worked. I slowly started to realise with the help of a Psychologist that they were never true friends. True friends don't walk out on you when things are tough, they are there all the time. Yes, it sucks. BUT I figured i'd rather be alone then have fake friends.
recently i had one "friend" go on a night out with me. I collapsed as I have heart and blood pressure problems. this so called 'friend' left me, on my own, with no one else around me knowing i'd collapsed and had serious health issues and I had to wait 30 minutes for my mother to get me... very scary. A few days later she told me that she wasn't bothered about the fact I collapsed, but she was bothered about the fact it ruined her night... well sorry that my mom asked you to stay with me until she got there. Needless to say, i haven't spoke to that person since.
I know its hard now, but you will meet new people. I've just started university and the people there are lovely, really accommodating of my health issues. Things do get better.
As for your boyfriend, again i'm sorry but do understand. I was with my ex 4 and a half years on and off. He knew about my health conditions, told me that he understood because he had mild Cerebal Palsy. It was only a few years down the line that things got nasty. Like your boyfriend, he wouldn't stop by to see me and made up excuses to go and see his friends all the time... or he'd stop by and tell me that he couldn't handle the fact I was ill, or that he treat me horribly and then would end it. What I didn't know was that he was cheating behind my back (or at least attempting to). We've been split up 2 months fully now, its hard as it was a loonngg time I spent with him and I thought he understood me more than anyone (he'd go to hospital appts etc) but I guess sometimes things just don't work out. Its difficult for us dealing with an illness, let alone other people and sometimes its best to get the stress out your life, we have enough of it.
I would look into relationship counselling etc IF that's something he thinks might help. My ex would never go down that route.
I hope things improve soon. Sorry I cant be of much help, just know that you aren't alone and that someone understands.