30 minutes isn't that long, could he not come up for the odd evening during the week if he misses you that much (or you go home)?
He's not dealing with this very maturely. Everyone gets busy at uni - yeah, ok, I do get worried if my boyfriend hasn't replied for a while and vice versa, but if that happens one of us will just say we're busy and we'll be in touch later, and I would never send him horrible messages like that. You haven't been away for that long and this could go one of two ways - either he will get used to you being away and things will be ok again, or he won't and he'll be like this all of the time. The first week or so of long distance after not being long distance is always difficult, so give it another few weeks. You're seeing him every weekend which is a lot more than many LDR couples do at uni.
Don't give him an ultimatum as such, but calmly explain to him that this is what you have always wanted to do, and uni is only for a few years, and you don't feel like he's living up to what he said about supporting you and you don't want to be with someone who doesn't support you in achieving your goals in life. Let him tell you how he feels about it but tell him he can't get angry as he does. How long have you been together? If it's meant to be it will work out between you, but only if he comes to terms with you being away at uni. Maybe he's worried you will find someone else because you meet so many new people at uni; maybe he's worried it will change you because a lot of people do change in some way at uni. That's not to say that you will do either of those things because it isn't a given, but he will probably know that it happens to a lot of people.
If he's jealous of your flatmates perhaps let him come to yours for a weekend so he can meet them properly? It might help with the jealousy.