I am probably a softie, but I think if he's toughed it out since Saturday and if by tonight he's not any happier, I'd just bring him home tomorrow. Fingers crossed you have a happier boy on your hands tonight and this isn't necessary. I think there is a lot to be said for not giving in on day one or two, but if things aren't getting better, day three onwards, I can't see the point of prolonging it. It's not like it's a school trip, where you do have to stick it out.