Crash and burned, stuck in the fire.

Hi I had a wonderful relationship and so I thought we were happy, until one day I caught my boyfriend with another woman. The woman is his friend's wife, they been having a 20 years affair, it was what ruined his marriage. When we met, he had broken up with her, then one day he brought her back into his life, he is afraid of what he was feeling for me and ran right back into her arms. In the meantime he continues to communicate with me through email, text, we do not see each other in person. I know he still cares, but we can never be together because of his desire for his friend's wife. I am in awe that his friend has no balls to stand up to that, I am sure by now he knows. I am struggling to let go and I still love him but I know that it cannot be. Since then I have tried dating and because of how I feel about him, I cannot seem to love anyone. It gets complicating, because we have finances tied up between us and so we communicate because of finance, but at times emotions are express. What to do?