Unfortunately that was the case for the girls in this episode. Marnie planned a perfect weekend with her friends to do some sharing and healing but her plans didn't play out. I think Marnie has a fear of change, and that's why she wanted a perfect weekend with her friends. When Hannah invited Elijah and his friends over to the lake house, that really freaked Marnie out. They where not part of her plan, and she just was not having it! Even though everyone else was having a great time with each other, not to mention Hannah and Elijah had a chance to catch up since he moved out. After they did the F-U dance, the fun was over. Marnie said Hannah could do her dance moves a little better, then it would be perfect, that was the finally nail in the coffin. At this point everyone was really drunk, except Jessa of course. And they just laid into each other. Well Marnie wanted to be honest, and she got!
The thing about being a true friend, you can't expect anything from your friends. You must accept them the way they are, and not want to change your friends. People are not perfect, everyone has baggage and problems. You have to realize that, otherwise people are just going to think you're stuck up, and a tight a##!