If I was in your position, I think I would finish the relationship. Not because the guy is a bad person, but because he's not right for you and doesn't seem to be giving you what you're after. Perhaps have one last chat with him about it all, but if it seems as though you're going around in circles and nothing's going to change, then call it a day.
You haven't been together for long; in a relationship that's developing healthily and happily, ideally this should be a time where you are both very much into each other rather than a time where feelings are being hurt and people are feeling second best. No one can tell you whether you're taking it too seriously, just as you can't say he's wrong for being too lighthearted and flippant about things. Everyone is different, and if you don't seem to match in that way then I think it would be really hard to get it to work.
I can understand how his behaviour appears insensitive, it would certainly upset some people. But it seems like that's just the way he is at this stage in his life, so let it be; I don't think you need to try and force him to change and behave in a way that isn't coming naturally to him. Maybe he likes more space than you and doesn't feel like he needs to see you all the time (remember you spend every night in the same building during term time!), and perhaps he doesn't realise that his jokes and comments are really upsetting you. Or, maybe he isn't happy either and feels like he wants out; perhaps he got involved when he shouldn't have.
It wasn't a good idea to get involved with a flatmate. But that's happened now and there's nothing you can do to change that. If you can end the relationship in a civil and adult fashion and give each other a bit of space, it'll be alright. Sure there may be a little awkwardness for a few weeks, but nothing you can't live with.
You may want to have a boyfriend, but there's no need to spend time with someone who isn't making you feel wanted, and who doesn't make you happy. University will chuck loads of opportunities at you for you to meet more people and make more friends, and perhaps the longer you stick with this guy, the longer you're denying yourself a relationship that you feel happy in.