I have not read everything you have shared, but from what you have shared your partner is very immature and you are constantly having your button's pushed to mother him. I know you have encouraged him to learn from the DBT book, however, at times he uses that as a way to gain attention.

He is not really "with you" as a partner, instead he is often competing with you which is what often takes place when a parent is raising a teenager.

In many ways you are his babysitter. You dread even thinking about him getting to have his children if you were to break up. A deep part of you knows he is not mature enough to really be trusted. He doesn't respect boundaries, not even with his own children.