She went to lunch with her friend and now she doesn't want to talk to me?

Okay so first off, I've known this girl for 5 years, we both from a small town so you pretty much know everyone in school. One day at college she popped into a class on the first day and sat next to me. We stated talking and became closer friends than we were. We started to go on dates and really had a lot of fun together! I would go when she was at work and hang out with her and talk. We talk almost everyday, until late at night. We've gone on a road trip almost a month ago, and she told me she really likes me and was excited to see where things go about three weeks ago. I always tell her how much she means to me and how thankful I am for her. She is always making my day better! Then a week ago she told me she was going to take her friend to lunch for his birthday, I didn't think much of it and said it would be awesome to do that. Then since then she has hardly talked to me. She only responds to my text once or twice, I've asked her how she's been and that I really miss talking to her and I think about her a lot and she'll skirt around it like "I'm good" where before she would send a meaningful message. I just worry because this friend she took to lunch was an old boyfriend and I'm worried she rather be with him, after she's told me that he's a creep. I don't know what to think. I've never had a bad day with her, and I'm always telling her how beautiful, and amazing she is. But it seems like none of that matters anymore. I just need some advice, what can I do? Thanks.