Whatever made up laws of friendship, ethics etc. you may think there exist, the ONLY valid laws are those of science and evolution finds a way to always fuck-up young male-female triangles. Always keep that in mind xD

You sleeping in bed with your gf and another boy and you not being the guy in the middle is already a big red flag btw.

It's not your fault though. Something like this is not worth to waste your life on.