I'm not so sure that you need to address the OM continued contact. You already did, right? In the letter you said that as long as he's in the picture you won't be friends with her.
I think it's always right to do whatever is in the best interests of the kids, I would offer help with them but don't know if that aligns with DBing principles or not.
M: 42 H: 43 M: 8 years S7 and D4 H has D19 and S25 from previous M Bomb: 3/6/14 OW discovered, EA & PA 1st separation, 10 days, decided to reconcile & moved back in. Fail 2nd separation: 5/1/14
