I'm glad your H felt guilty and treated you nicely.
What about making a list of boundaries that you need respected if he is to stay in the house? Then, put the list to him in order to avoid any further confrontations. If he can't abide by what YOU NEED, then so be it. It will still be his choice.
My D19 did this with her dad over the summer. She told him he could only move her into her dorm IF he went to four A.A. meetings or went back to counseling. He refused. It's given her some power because whenever he brings it up, she is able to say, "Dad, that was YOUR CHOICE. You refused to get help. That's not on me." I was really proud of her and it puts the responsibility back in it's proper lap.
Your H needs to know it's absolutely NOT OK for him to carry on with this affair in your family home. What would happen if he left? Maybe spending unlimited time with the Gnat is just what he needs and deserves.
I'm just thinking out loud. Take what you like and leave the rest. Maybe I'm just angry about my own sitch today.
Much love and so proud of how you stood up for yourself!!!!
Heather
"You know, it's times like these when I realize what a superhero I am." Tony Stark/Iron Man
“Focus on what you can do, then do it with all your heart.” Lois Wilson