He's sharing a hotel room with his ex?

We've been together for half a year now, and we love each other very much.

Tomorrow he is leaving the country for a business convention, which I've known about for quite some time. So has he.

The problem is that he will be sharing a room with his ex-girlfriend/boss! They will not be sharing a bed, and I'm sure nothing is going to happen, but I'm upset. They are also driving there and back together. What, if anything, should I do? I've told him I'm uncomfortable and he says that nothing will happen and he cannot afford another room.
He's sharing a hotel room with his ex?
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