is she going alone of with friends? That's a big difference. Relationships are based on trust and communication. If my GF wanted to go with friends, I would be hesitant but I trust her. I would obviously ask why we can't go a different time but if it was a planned trip with her GF's then whatever, I trust she won't do anything. Mind you that we would've talked about this first. The red flag, for me, is the fact she bought the ticket and was going regardless. Has she ever done anything to think she would cheat? do you actually trust her? it's ok to be bothered by her going "alone" but I would be bothered by the lack of communication more so. Sure, trust is earned and in 2 years I would hope you trust her otherwise why be with her? if you trust she wont do anything and she's going with girl friends, I don't see a big problem but definitely sit down and talk about how upset you are that she didn't consult with you first and how you had planned on going together. If she truly is going by herself, then I would oppose to it. If you just don't trust her going, then you need to re-evaluate the relationship.