Don't know why I feel this way

So the other day I was on my fiancees facebook checking his farmville account for him. I harvested a few things, plowed..whatever. Anyway I forgot I was on his profile and saw there was a message (thinking it was mine). I checked the message and found a conversation between him and some other girl planning a day downtown doing "Tacky tourist" things and then going to Don Cherry's for supper. When I realized it wasn't meant for me I felt immediately enraged..Why I don't know, well I guess it was because I felt like he was planning a date, never mentioned me, and since my ex Jon cheated on me I kind of feared the worst.

Maybe it's my trust issues, but I can't shake this feeling that this other girl is trying to move in on him. I dunno..I just can't help but feel left out. I finally asked him about it, he said they wanted to go hang out downtown, and that I could come to dinner with them..Yeah that would feel weird, sounds like he's afraid I'll be a third wheel. I feel tempted to look and see if there are any new messages, but at the same time I am not sure if I want to look. I'm kind of afraid of what I'll find.