<human>: Summarize the given text in a few sentences.

I'm a little more than halfway through a 2nd week of feeling uncertainty and weirdness with my gf of 6 months. I tried talking to her last friday and most of the answers to my questions of trying to figure out what the deal was, were: "I don't know." and "I don't want to talk about it." She's been on vacation with her parents since Sunday and we've had a minimal amount of texting everyday up until yesterday when I didn't hear from her at all. I feel completely helpless. I can't think of anything that could have caused this weirdness leading up to when it started a few weeks ago and it's killing me. We even bought plane tickets to go on a trip together in October a few weeks before this all started. I'm 28, this is the longest and most successful relationship I've had, and the thought of it ending is terrifying and making me literally sick to my stomach.
<bot>: My GF has been acting distant and "blah" the last few weeks. When I try to talk to her about it, she doesn't have answers and doesn't want to talk. I don't know what to do.