I'm sorry, I haven't followed your situation up to now, but your question caught my eye.
I would gently tell him, along with the circumstances. He can't heal his relationships unless he knows the truth. And you can't heal your relationship with him while a secret like that is gnawing at you.
Best wishes to you!
Me42, H40 D12, S8, S7 A revealed: 7/13 Sep 4/14; Agreed to D 1/15