He is a big boy. He is making this CHOICE for a reason. Maybe, just maybe it is a thing call love. He loves you unconditionally. Which makes me think of two questions.....

1) Would you do the same for him? If he was totally messed up - would you stay with him? Forever.?

2) Will you accept his love?

Nothing else matters (in my opinion). To me - it sounds like you have a keeper.

and by the way - CONGRATS to you