Let me get this right...
You are going to meet your girlfriend in 2 weeks on the train which costs 30 quid. Then you might not see her until December or January. So a mate has offered to go on the train and escort her to his party for Halloween. This will cost 60 quid. And then you get to play hide the sausage.
Right?
I've read the quite frankly outlandish replies to this thread, you should be ashamed, yes you, but i think i agree with their disgusting thoughts.
If she won't travel on her own, the freak, and you can't afford both fares(why can't she pay for once the cheap woman) then borrow the cash from your mate rather than letting him do it.
If he goes to get her you might find that sloppy seconds is not a nice thing.