Just get his arse fucked
Then say three Our Fathers and two Hail Marys and all shall be forgiven
only if he's genuinely sorry for what he did - otherwise, absolution is not possible
I suppose if you were really keen on avoiding sin, the fact he's married isn't really the biggest issue . . .
looking at it from an ethical standpoint as opposed to a religious-moral standpoint, it's still wrong. Consider that violating the sactity of their marriage could harm a lot of people, not just him. You would be every bit as resposible.
From what I've read of your exploits, you don't seem to have any problems getting some. Just move on the the next hunk waiting in line . . .