<human>: I've(18M) been with this girl (18F) for six months, we've been through a lot. 

Stood by her side throughout a major surgery, and two months of missed school, I've always been there for her.

Within these last couple days, I've started feeling like she isn't into anything anymore. We rarely have sex, she rejects the longer, more passionate kisses, and as of last night, I saw her texting a guy when I was driving. 

I asked her about it, and she said it was "someone who graduated with her brother, years before. I have a lot of respect for him, he's a friend". She's texting him because she's going to his birthday party.

I looked the guy up online, and back in February he posted a status asking if he threw a get together, who would want to come. My girlfriend said, "me".

I told her I don't want him flirting with her, I don't want him saying good morning or goodnight, and she said he doesn't do that good morning / goodnight stuff. So I said again, I don't want him flirting with you, and she said he isn't. Also, I told her to make sure he knows she has a boyfriend. She says he does. 

I don't necessarily want her to have a guy friend to talk to, all buddy buddy. Is that bad of me? I'm pretty jealous, and I'm ashamed to admit it. 

I have cut ties with all of my old friends that are girls just for her, to ease her mind that she is the only one for me. 

Am I overreacting, Reddit? Should I tell her I don't want her to be buddy buddy with another guy? I am lost.

Can you condense the text into three sentences or less?
<bot>: girlfriend texting/ going to another guys birthday party. Am I overreacting by not wanting her to be buddy buddy with him?