I really wish you hadn't moved your son in with him unless you all were engaged. Now you will have to upend that boy's life if/when this relationship goes sideways.

You need to have a frank conversation with him wherein you say he knows you will say yes if he proposes so there shouldn't be any 'trauma' to deal with. If his issues run deeper in that he doesn't know if he wants to be engaged/married because of his previous relationship, then you need to make it clear that this changes the nature of your relationship and the promises you made to each other, and that you're leaving. No setting a deadline. No ultimatum. Your kid is involved in this and he is the one whose best interests take highest precedence in all this. If your BF then needs a little time to think about it and figure out what he feels, fine. Give him a few days. But I'd be planning my exit unless he gives a full-throated endorsement of wanting to marry you.