We just need a dead rabbit.........and all will be well!!!

Like everyone has already said, let it go.

This is a no win situation for you. If you find out he is dating/sleeping with someone new you will just be hurt in the end. If you find out he is not, you will feel like crap for doubting him with little or no proof one way or the other. He won't be thrilled with your actions either way.

You have both chosen to be "friends" for now, would you want a "friend" interjecting into other parts of your life without permission? Being a "friend" involves a level of respect for someone. Sadly i would have to suggest, if you can't stop these types of feelings.. might be better to drop even the "friendship" part.

sounds like you are still holding on...

And a big pot. And a stove.

If you feel it, trust your gut. If you trust your gut, you already know the answer. If he wants to end, your angst won't bring him or what you hoped to have with him "back". Like you said, it was over a long time ago.

You will make your own decision in the end.

No one can decide for you; but finding out he was betraying you all along won't change the outcome. Most of the time, it won't bring closure, either. What it will bring is upset towards yourself. You know that.