My question. Who is he likely to be more honest with; you or her?I didnt want to be on my own so I took the dogs and moved over to be with her.
Either he doesn't want to tell her he moved back with you for love; because he's keeping the door open for her.
Or, he was honest with her and moved back with you only for the convenience.
Either way - not good.
There's no reason for them to have any contact. That's a boundary that he has to accept. If he doesn't, divorce him. Continue to monitor him if he agrees.
As for as his tepid reasoning to her about moving back with you; I hope all his actions toward you suggest otherwise.