I think I would try a couple sleepovers and see how they go before doing it on a permanent basis.
Peace, sometimes they are very honest about their new spouses and sometimes they aren't. Look at my xh....I've only tricked him a couple of times in 10 years to even admit he's married. He never mentions her when he communicates with me...it's always "I did this, I traveled here or I go here"...never "we".
Let him go. He's no good to you the way he is. After all the ow has given you a gift...she's taking care of him while he's ill. You didn't need that full time in your life or your kids' lives.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.