J.,
I guess it would depend on whether you are becoming your boyfriend's partner or roomate.
I was with my boyfriend for 2 years before we decided, together, to bring our kids under the same roof and become a family. We absolutely needed a bigger house than the one I currently was in so we began looking, all of us. When we finally decided on one we got the mortgage together and all of the bills are OURS.
I have 1 child and he has 2 with 2 others spending weekends and holidays. There has never been a question of who uses more space, electricity, water etc.
We are a family. I guess that's the subject i would bring up with him. If you are creating a family then your are partners. If he still has the same issues then maybe he sees you as not a partner but a roomate.
Best of luck. Talk it over and make sure your expectations of the arrangements are the same as his before you commit to a move.
Take care