Well, were they naked?
Also if they are friends that means they have some kind of history. It very well could be fully platonic. I have female friends that are totally platonic. Also while they were in bed how much space was between them? None? A foot? Even then that is still only the part of the picture you see. You don't see it all. Now if they were going at it and not sleeping then I would say "BUSTED" but frankly sleeping on a couch is not all it is cracked up to be.
I know guys that when they travel sleep in the same bed to save money. They are FAR from gay but I would not sleep in the same bed as another man unless there were some unusual circumstances afoot like it was WAY past freezing butt assed cold and there was no other way to survive.
People are just tooo F@%&ed up over sex and fidelity!
Unless caught in the act two people in bed means nothing unless they are naked and you can smell the aftermath and believe me unless you use a LOT of air freshener you can tell when two people have been doing the wiggly. Sweat, pheromones, the dew of down below, messed up bed, I mean come on, there is more to life than sex!
It is just that good sex is fun and a little harder to find than mom and dad ever had the courage to explain to us when we were younger. Just don't try looking too much into anything sight unseen. Jealousy is just screwed up and not good for anyone. If you got to question someone in a relationships fidelity with you you need to move on for the piece of mind for everyone. It means you are in the wrong place in your head for a friendship or a deeper relationship. Some people thrive on that kind of drama though.
What if your friend really was getting all Frita Callow behind the scenes on everyone? Gonna end a friendship over her life choices too?
The first time a friend of mine admitted to me he was gay after I was out of high school was a little shocking but we were just friends. It explained why he acted so girley all the time but he was not a bad person by any stretch of the imagination. I could not see tossing aside a good friendship for his choices in life. As long as they don't drag you into something that you feel is wrong then there is nothing wrong.
I know this is nothing like what you are facing but there may be realities behind the scenes like what if she was sleeping in the same bed as her brother (cloths on)? Now if they were naked all I can say is this...
CALL JERRY SPRINGER IMMEDIATELY!
Remember, Jerry Springer Loves You!
Wow. In deeper thinking this is a can of worms for you!
Hope the best for ya!