Most Helpful Guy
She was two years of his life. You may not like it, but you can't change it. His time in that relationship has partly formed who he is. It is a part if his history, his life story. Now you are also part of his story.
If you try to erase that history you are trying to change his identity, and understanding of himself. Not only will you fail (you can not info the past) you will also piss him off, and present yourself as jealous (not attractive), needy and high maintaince.
Either choose to trust him and stop worrying, or accept that you are too immature for a relationship and move on.
Most Helpful Girl
Yes there an ex for a reason cause if there still up he not over her or they still shacking up without your knowledge.