This scenario crops up often on here - as do the responses, which can be boiled down to -
He's a rat for doing this, you could never trust him ... etc.,
but from what I gather, you love him, and maybe he loves you too, but we can only address your side, because that it what we have.
I always remember Nigel havers, who left his wife for another woman. The media, because they are as shallow as their readers, kept equating him as 'The Bounder', a character he once played on TV years ago.
He was interviewed on TV and said "I didn;t go looking for this ... I have to deal with it ..." and that is more real than any 'Bounder' secnarios that surrounded him.
We don;t choose whom we love, or the circumstances that surround them. It's very easy to look down from the moral high ground, but intellectually, you know all those arguments perfectly well.
It's emotions that work here - no respecters of commitments, or circumstances, the emotions will have their way, and will never listen to reason, from us, or from anyone.
What do you do?
Move on. Impossibly hard, so very painful, but still the very best thing to do. This man may say he loves, you, and it may be true, but he may be dealing with issues he doesn;t understand, and looking to you to provide a get-out clause from his fears and his feelings.
Don't let him leave to come to you. Let him leave, and come to you in six months' time. That way you know he is there for you - if he stays away from his wife that long, maybe yoiu have a future.
I hope youo work this out. Love is wonderful, and cruel, often both at the same time.