To set the scene: friend X is my best friend of years. We used to live together and have lots in common and great fun together. She moved 100 miles away two years ago and now I see her about every two months.
Friend Y lives in my city, and is friends with X from when she lived here too. Y is a nice person, but quite different to X and I. Since X moved away, Y has wanted to be involved every time I meet up with X, and to be honest I hate it. She came to a festival and wanted to go to bed early every night, patronised me saying I am too drunk and tried to take me home from a party (I was with lots of friends and completely safe), asked to come on holiday with us then completely steamrollered our plans because she couldn't afford them so we had to stay in a hostel instead of a nice hotel, and so on. She's also quite passive-aggressive - she wheedles and sulks instead of just asking for things her way. If she doesn't get her own way, she makes the atmosphere horrible. I do like her in small doses but I don't ever want to spend days stuck with her again, and usually mine and X's meet ups are for a weekend or longer due to distance.
X is really easy-going and when asked, will always tell Y our plans. I really want to be able to spend time with X, without Y there being a killjoy. X likes Y and wouldn't want to upset her (nor do I).
What can I do? Am I just being a bitch?