“so our relationship has been very much like a marriage to me.” If you’re committed, don’t let him go.

If you’re scared of his daughter make sure he knows YOU are scared for you. You said you are setting the boundaries to protect you all but I think you should just focus on protecting yourself and let him deal with her in his own way. It sounds like the kid needs intensive therapy but if he’s insisting on having her visit he obviously doesn’t have the same fears you do. He’s afraid of losing her.

In five years if this is over there will be something else you have to work through. There always is. Maybe, hopefully, not this Big or intense, but it will be something. Love yourself more if you need to. As far as the relationship you wish you had any little step you can take to make it happen is in your power.