How do I act?

[steady]

I would imagine it's normal for them to dive right back in sometimes. I think Michelle addresses this in her book as one of the three things that may happen when you DB.

Take your H lead and go to the pastor for some counseling. You may need some professional marriage counseling also. I don't know because each situation is different.

Remember how you felt when your H dropped the bomb? Maybe you drawing that boundary and being totally willing to walk away from your M was a bomb for him. Didn't you jump right back in and try to 'fix' things?

You're outside my area of advice as my sitch went south and continues in that direction. Hopefully someone who has some experience in this area will respond to you.