Live with two flatmates.
One had his gf staying last night and she always leaves house later than any of us. She generally goes out through side door and posts key through letter box. Not a system I promote but one I have begrudgingly agreed to tolerate.
Anyway today I return home early and front door won't budge; it is clear she has left latch on and gone through (locked) side door... I tell flatmates and one comes to help but one with gf stays out, sleeps at friend's house and offers no support. Bill comes to 300 quid. Who should pay? I am close to snapping...