Note that "spend the night with" doesn't necessarily mean having a sexual relationship (though I'll grant you it does sound like it can be the setup for some bad porn fanfic story).
She was assigned to him while he was aboard Melek's freighter, and he accepted the offer to not give offense. Never mind the issue of personal safety (no small concern when in a ship full of 7 foot tall carnivores who tend to react rather poorly to things perceived as insults), offending his hosts wouldn't have helped his efforts on behalf of the UBW.