And yes I realize he's been gone for a long time, but he hasn't processed the affair... he's escaping the damage rather than healing it...

He thinks having a revenge affair and hurting YOU is going to make him feel better... It won't... He can escape the hurt YOUR OM brought into his home for a while, but it will keep haunting him...

I am hoping a FT offering to help him process might make some inroads... You need a neutral party to motivate him to talk about what he's been through... a GOOD FT is ideal, a close marriage-educated friend is a good alternative...