It might make sense to consider creating a lease for your boyfriend. I know it is uncomfortable to do this, but even if you charge such a small amount that it is negligible on a month to month basis you're going to be more protected in case something happens or goes wrong. Include the number of overnight guests he can have and for how long in that lease. If his guests end up staying for a long time they can end up with some rights/ you'll have to legally evict them (which is a huge concern given it is his family). If you're the one buying the house, you're the one taking most of the risks (really all he is losing out on is building equity, he can peace, stop paying, destroy the house, etc. without the consequences you face), he needs to understand and appreciate that component of this. He also needs a reality check in regards to what parenting is like.

Also if you're about to live together and have kids together you need to work on your communication. The way he handled all of this is indicative of not great things, as you've probably already realized.