Sorry to be a thread hog...one more point...DON'T let this drag out for 1.5 years and worry about this guy the whole time...it just holds your marriage back and makes reconcilliation a LOT HARDER.
This guy is just homewrecking at this point and he knows it...the fact that he won't walk away when he's clearly not welcome leaves me viewing him as nothing more than a sociopath.
Anyone who enters' someone else's life, their home, or the couple's life and THREATEN's that in any way is nothing more than pond scum. Marriages are hard enough to make work without this ass hammering away at something terribly delicate.
He isn't worth an ounce of your time, he's behaving like a spoilt child who has been sent to his room. Let him go and enojy your devoted and generous husband. I admire his courage and strength, not to mention his devotion for you. That alone should be attractive enough for any woman.
In my opinion, your husband is more than a partner, he's a god damn romantic. Love him like he loves you...that's a rare gift he's offering you...love in the face of betrayal...don't take that lightly..its NOT easy to take someone back into your heart when they played a part in hurting you this way.
Your husband's one in a million. Love him, and let the rest of it go.