I'm annoyed and potentially planning on ditching my friend at a music festival
Is there a particular reason why you could be annoyed?
I would rather go home early, we are really far from home.
If you want to go home early you need to let your friend know because it can be dangerous. If you are the only ride home you should make a plan to not leave them stranded.
Fine I won't leave them.
Thank you, I bet they will really appreciate it. Next time if you have to go far and don't want to you can decline the invitation.