I would do this:
First, call the boy's parents, explain the situation and ask them what they think you should do. He's under 16, so is still their responsibility. You never know till you ask, but they may actually come and pick him up, in which case, problem solved.
However, as sounds much more likely since it's now gone midnight, simply put him up in a spare bed somewhere, but not obviously (!) in your daughter's bedroom. Are you honestly saying that you are incapable of keeping them apart until morning? Surely not...