It happens... when someone cares about you, hearing something like that can make you angry. It scares you... you want the person to be happy, you want them to realize that they are important to you... and when they tell you that they don't feel like existing, it's almost as they're not even considering the relationships that they already have. Is it selfish? Who knows... I could argue that your boyfriend was being selfish for yelling at you because he doesn't want YOU to be selfish. What's the point in pointing fingers? We all want to be happy... so what's wrong with having problems and needing help? I would think nothing.
So putting aside whether or not you're being selfish, I think the point is that you're having a hard time. He may not have dealt with something like this before, and so he doesn't know how to respond. I think the best thing that you can do is, when you feel ready, explain to him. Tell him that you're going through a hard time, you just wanted his support in helping you through all this, and that yelling doesn't solve anything. Honestly, his yelling has most likely made you worse, because it only furthers the feeling that you're not necessary in this world...
I think you have a right to be upset. There's nothing wrong with that... it's ok to be sad and need a helping hand, and sometimes... we get hurt by opening up. It happens... but you just need to realize that YOU're trying your best, and you're doing what you can. If you do that, then no one can expect any more from you.
It's tough to deal with, especially with all the changes in your life. As others have said, you may be experiencing depression, and that can take over your world, and you depreciate yourself... give yourself time. Hopefully things will look up. Since you're in college, consider looking into the counsellors that they have there... it may help you out a great deal.