No, it's not too early. Especially since your situation is basically forcing your hand, there's probably no better time to move in with your boyfriend. Whether you've been together for four months or four years, there's still going to be a level of adjustment to fit your habits with his. Basic instructions on how to get along with a new roommate are:
1. Make sure you have some place to avoid boyfriend when he inevitably annoys you. A room, a nearby park, or just a car or bike to get the hell away for an hour or two.
2. Communicate your needs and wants, and listen to his.
It sounds like you're not going to be entering into a lease with him immediately, which is good since it leaves the option of escaping if it turns south. Are you going to be staying at his place during the summer when he's traveling?