What a hard situation! Thankyou for sharing your story, I hope getting it out has helped you a bit.

I couldnt break the heart of my lover if I ever cheated on him (one of my biggest fears is going manic and cheating - its the reason I stay on meds and worked so hard to not have an episode since being with him) I dont think I could ever share this secret, especially if he thinks the child is his. If he leaves, the child is the one who suffers, along with his heartbreak of losing a child that was never his.