It sucks, but some people really do have trouble falling asleep around others, and then there's also really light sleepers that struggle to stay asleep in the same room as someone else. I've slept in a different room to my husband of 9 years for a long while now, and we both sleep so much better this way. It doesn't mean I love him any less.

I have that issue sometimes. When I have to get up for work in the morning and I'm trying to fall asleep but they're snoring or won't let go of me (arms wrapped around me and I can't move) I find it hard to fall asleep. And I'd rather just sleep on the couch than with him. Some people sleep a little more snuggled than others. Some hate to feel restricted. She didn't do anything wrong by wanting to sleep on the couch. You are probably doing something that's keeping her awake. She could have opted to move back home. Then you'd be even more upset. She still chose to stay at your place, so be happy you have a girlfriend who likes you enough to be with you and to sleep on your couch rather than have her own bed.