Did everyone at his company go to NO? Was it a team building exercise? I can imagine "the new guy" isn't going to want to refuse to attend.

Or was this a reward for good performance? Did only the best performers get invited? In that case, you asking him not to go may feel to him as undercutting his accomplishment.

Again, not saying you should accept business travel. You feel how you feel and you are entitled to set your boundaries wherever you need them to be.

But I can imagine several scenarios where he would feel a substantial lack of support for his career. Doesn't mean he is entitled to ignore your feelings. Just saying that you need to be mindful fo his, as well.

When you can see it coming, duck!