well, even if you do get attatched to this vienna girl. at least you know ahead of time that it is a possibility, and that you know you won't see her again for quite a while.
with that said.. relaxe and take life one day at a time
what happens happens, and theres no sense worrying about something that hasn't happend yet.
i think you might be working yourself up to a point in which you'll be so nervous that you won't be able to enjoy yourself while your there. its only a weekend right? kick back, enjoy the companionship, see vienna, and expect nothing
just my personal opinion