As Chris says, the act of disclosing can have hidden consequences. It's like peeling back the layers of an onion. Everytime you think you've got the thing peeled there's another layer lurking just underneath. Some of those layers contain some pretty heavy consequences or unexpected healing of relationships, and it can be hard to tell which it will reveal till after it's done.
Perhaps you and he need to read an article here on the site about Disclosure and Confrontation.
I think it will help both of you to understand the undertaking.
Your BF is correct also when he says it's his to decide. You may share with him your views in a nonconfrontational way, but ultimately it is his to decide.
Best wishes to both of you as you work your way through this difficulty.
Lots of love,