I think you must leave him law. Caused he can date you when he has wife, even you get away, he also will treat other girls like that. To get rid of any suffer, leave him is the better decision.
正確, cuz all of us know that if he divorced with his wife with him, and it will bring to an unhappy end. And it usually brings to a tragedy. Remember princess Diana? Her ex-husband had another girlfriend (Camillla) and they divorced. And at the end Diana died, which is a horrible tragedy. And Princess Diana ever said :" 一個婚姻裡有三個人,實在太迫了."
And Diana is the symbolg of the tragedy of 三角 關係. So before it is too late, get out of it! Anyway, you and him never have anything happern,right? But he and his wife may love wach other very much! And anyway, if his mum knows that He divorced with his wife because of you, What will she think? Do you think she will accept you?
Hope I can help u, ask God to help you.