Long distances are hard on the relationship, and if you can only manage to keep up a conversation every month or so, I'm afraid it looks like it's not for you. Maybe when you get back to gether it will be like before, but for as long as you're apart, it seems your partner isn't capable of mantaining the commitment.
You might want to increase the frequency of your converstation, go for actual speaking (rather than writing) or IMing, but he might feel you don't trust him and use this as an excuse to drifting even further away.
I think the best thing for you is try to let go. If this is the interaction he (and you) are capable of, there is little that can be done. Enjoy the summer, let yourself get to know new people, make new friendships. If by the end of the summer when you meet again all is well between you two - great! if not, at least you didn't spend the whole summer pining for him.