<human>: Hey guys, just posting because I'm kind of lost here as to what is normal and if I'm being over sensitive about this. I'm currently dating a great girl, who happens to have a twin brother who I am also good friends with. 

The twin brother came over this weekend and I offered him a sleeping bag in my room but he said it was ok and he'd just sleep in his sisters (my girlfriends) room. I assumed he would sleep on my girlfriends roommates bed, as she is gone for the weekend, and my girlfriends roommate was ok with it, but this morning I went to the room to find them sleeping in the same bed together, the brother shirtless and my girlfriend only wearing a long shirt over her underwear. I know they are siblings, and I don't think it's a huge deal, but something about this rubs me the wrong way. 

There have been times where they've shared beds before, for example this summer when her brother didn't have his mattress for a week or so and they shared beds, and I wasn't able to FaceTime my girlfriend like we normally do at night. This was fine of course as there weren't other beds to sleep on, and I didn't think he should need to take the couch. 

However, this time there was a wide open bed literally five feet away! I dont believe there is ever anything between them but I don't like the idea of my girlfriend sleeping half naked with some other guy in her bed, especially if there is an open bed available so close by. I haven't said anything yet as I'm not sure if this is common or not, and if it is I guess I need to just get over it. Can you guys help me with this problem?

Can you condense the text into a few key points?
<bot>: girlfriend sleeping half naked in same bed as twin brother with open bed right next to them, bothers me a little bit, not sure if this is normal or not. Help!