<human>: Can you condense the text into three sentences or less?

Last night, my (24M) girlfriend (21F) of seven months was staying over at my place. 

I know that this one guy an ex-FWB of hers is still after her, and after she went to sleep I stupidly checked her text messages. Sure enough, this guy has been flirting with her over text, that I expected. But I also found out that this past weekend she agreed to meet up with him for dinner. She never mentioned this at all to me. So I didn't sleep well last night and couldn't stop thinking about everything today. 

I know what I did was wrong, and I do feel bad about it. But what I found has really upset me. When she left this morning I put on a smiling face but I was being eaten up inside. 

I like to give people the benefit of the doubt and it's possible that nothing happened and the last thing I want to do is to ruin a good relationship because I'm overreacting. Still, I'm pretty hurt that she didn't tell me about this. I feel lied to. Am I wrong to feel this way?
<bot>: My girlfriend didn't tell me about messaging/spending time with an ex-FWB and it's really hurt me.