Sounds pretty troll like, BUT if you're not a troll... Don't say anything about the trip. Make him aware that you the truth, but don't be angry about it, cause like you said, you're not even a couple yet, you have no right to say what he can and can't do. Let him know, you know he was lying, and tell him, "we're not exclusive, you can see other people, just don't lie to me about it" and when things start to get serious, you HAVE TO have "the talk." Some couples don't need it, but in this case you will. IF things get serious, you'll need to let him know that you don't intend on seeing anyone else, and you expect him to reciprocate.
May the wind always be at your back and the sun upon your face. And may the winds of destiny carry you aloft to dance with the stars