Why would he bother to come around and see you while dating the OW?
Probably to feel less guilty. As long as W is fine, he is fine. He is also having his cake, and eating it,too. He has a girlfriend and a wife, and wife seems "ok". I wouldn't do anything that'a like a date with your H as long as he is with the OW (eating out, taking walks, etc.). He's not feeling any of the consequences of losing you. That's just my opinion, though, it may not be DB principles.