While your H is involved with OW, YOU do not meet his needs. When I say dint be a doormat be the door I mean show him that he needs to either walk through it or stay inside...........
He needs to know your not going to live in an open marriage. THAT is a boundary for your sanity and well-being. Whenever he brings up OW tell him "I am not going to live in an open marriage" and either walk away or hang up the phone. If it is a text delete it and don't respond.
You are nothing more than a co-parent right now, show him that. My H used to text non stop, I felt better when I would ignore everything all day and respond to the important things in one text or email at night.
Me: 35 husband:39 Sons 16 and 11 from my first marriage Twins 5 (boy/girl) Daughter 3 Affair bomb 2/27/14 He moved in with ow 3/13/14 OW kicked him out 6/15/14 4/2016 he seeks help for sexual addiction