Bring this up to him immediately! This is exactly how my last relationship fell apart as bad as it did because I didn't bring it up. I simply just accepted I was replaced and left without a word. I had no closure what so ever and, 4 years later, I still feel like I need that closure.

Please talk to him. Even if he starts to steer the conversation away, make him keep talking about it. Maybe get his best friend involved since he was suspicious too. Even if it's just a misunderstanding of some sort, you wont know until you talk to him about it. Communication is key to every relationship, and even if it makes both of you uncomfortable with the confrontation, it's definitely needed right now.

I don't like seeing other girls go through the same thing I did, and I will go down in a blaze of glory [or not so glory] to prevent them from making my mistakes. Please please talk to him about all of this. Maybe just print out what you wrote and give it to him. Sometimes people are able to express more with written word than verbal. Find some sort of ground that you guys can use to talk this out.