Should I expose the affair to her husband?

You know... You've take enough from this A**hole long enough. He's had his chances and blew it.. My suggestion to you is it is time to cut the ties that bind and start a new life. So calmly, tell her hubby, because yes he deserves to know, gather a few of your former friends together and quietly, calmly lay out the truth for them. Tell them that you wish things could have been different you could have remained friends but that's life. You need to move on.. Then take the actions that you need to to remove him and all remnants of your life with him from your future. It will be painful but for you to heal and find your soul mate in the future it is necessary. Good Luck to you. You deserve better. Living well is the best revenge!!!!!