A bit witty today. Someone must have gotten laid last night...lol.
OP - stop thinking about everything so much. Just talk to her straight up...see how the convo goes. If your GF doesn't want to have sex much anymore she may be feeling the same way? If you both decide to give it one more try then go for it...if not then break up and move on.
I still don't understand girls who can just talk to some drunk dude at the bar and then take him home and **** him? Weird and gross...