Re: I need help with a BPD girl I love.
The situation of her spending the night at her ex's house, for WHATEVER reason, is no good (in my opinion). And on top of it, she didn't show much respect for you because she knew you didn't really want her to do that, but blew it off and did it anyway. That just sounds sketchy to me. Maybe feelings for the ex are resurfacing.
Anyway, my suggestion to you would be to just talk to her. Tell her to just be completely open and honest with you, and not to string you along or play games. Communication is so very important. Give her some space, but ask her why she suddenly wanted a break. And don't let her take advantage of you.
As a side note, I don't think wanting a "break" always means goodbye. I once wanted a break from my boyfriend because he was smothering me and I needed to take time apart to decide if I really wanted to commit to a relationship with him. (We were about 4 or 5 months into our relationship) We got back together after about a month, and I'm SO thankful he waited for me during that time. I never wanted another break after that.