No one deserves being outed. Period. However, you were incredibly insensitive to interfere with your friend's grieving period. No matter how difficult his ex was, he cared for her and she left him. Being the one left behind is devistating, and your time together should have been all about him and his feelings about his situation.

If you ever find yourself in this situation again, don't have sex with the person, and don't confess your feelings to them. Give them time to work through their own stuff. It's what a true friend would do.