LTR traveling without me, considering break up

Sorry for my English, I'm not native.

I've been in LTR for 4 months she's 22 and I'm 23. Everything seemed great so far. We've been discussing traveling to Asia when I finish my semester. And now all of a sudden, without telling me anything she booked a flight to Singapore for herself. She is gonna stay there for 5 days. Even though she told me to come with her, she knew that It's impossible for me because of work and university. I'm considering ending it with her. She's going to stay in a hostel, also I saw on her phone that she has the couch surfing app... She said she's not going to go clubbing and bars, but I don't believe she's going there to learn about the culture and stuff. The only problem is I really like her, because everything else was good.

Do you guys think I'm overreacting, or what would you do in my position?

TL;DR LTR traveling alone to Singapore, how to handle it?

EDIT: Thank you guys for all the advices, I'll not have too much time during her vacation due to exams and work, but I'll try to set time aside to meet some girls. I'll prepare mentally for letting her go, but first I'll see how she communicates during the trip and how is she when comes back.