<human>: Me and my gf Katie go to the same college, where we met, and we've been dating 3 months. Her male friend Nate also goes to school with us, and he met her around the same time I did. Katie and I are currently long distance for the summer since I live out of state and she + Nate live in our college town.

First of all, Nate is the kind of guy who only hangs out with women. Every day at school he would eat lunch and dinner with the same group of 4 women, and until we started going out Katie would have most of her meals with them too. She started eating dinner with me when started dating and would eat most lunches with Nate + his group. Which was fine with me because I know it's healthy to not do every single thing with your girlfriend/boyfriend and I am not the jealous type, within reason.

But it seems like every single time Nate would go out out, he invited Katie along. Every movie, every late night Sheetz run, every study session, she would get the invite and go hang out with him and his little harem. Now that we are long distance and I'm not around, she is spending even more time with this group.

Now, to the point of all this. She had told me she wanted to go to Nate's house to watch a tv show and I said okay. Then afterwords I find out through the conversation that they didn't watch it in the living room or other common area, but in his bedroom, sitting on his bed. This dude was sitting shoulder-touching-shoulder with my gf and this other girl on his bed for several hours. 

Am I wrong in thinking that this is out of line? I think it's common sense not to be in bed with another guy when you are in a relationship. Katie is annoyed at me because she does not see the difference between sitting next to each other on a bed and sitting next to each other on a couch, and she insists that they are just friends. Is this just a weak excuse? This is my first serious relationship and I am flying blind here. Please help.

Provide a brief overview of the text.
<bot>: Girlfriend has a male friend who she insists is just that, but they watched TV in bed together last week. Is this cheating/crossing a line?