The first thing you have to do is get rid of the anger. Anger is a primal defensive mechanism. It is suppose to protect us from harm. You need to loose it, and all the assumption that comes with it.
You are assuming that he's lying to you, you are assuming he is trying to fool you. You are assuming they are planning to leave their spouses and planning to be together for ever. Stop assuming things about which you have no proof.
Finally, when you stop being angry, and you stop assuming, you will be able to stop viewing everything he does as a personal attack upon you. His actions are not about you, and maybe that is another part of the problem --- that you feel they should be more about you. His actions are not directed to hurt you, but to ease whatever hurt he has within.
