Ask him why

You shake your head in disbelief. "Why would you do this? Why make a fool out of me?" You start to pull your shorts back up, but he catches you by the arm.

"I wasn't trying to make a fool out of you," he says. "It started out like I said, as a test. I needed to know if I could trust you. And then I saw the shower, and you were so kind, and... and it's been a very long time since anyone was kind to me." He sounds so sad, so lonely and desperate. Of course, that might be an act, too, but you don't think so.

"What about your 'mission'?" you ask, not yet willing to fall for another of his lies. "Or was that a load of shit, too? Did you just come here to get laid by the first idiot human you could find?"

"No, what I said is true," Luke says. "My team came here to gather information, but we had to abort the mission when the police showed up. They went back through the portal; I'm trapped until they can come back for me. I'm alone in this strange universe and, frankly, I'm scared to death. I shouldn't have tried to trick you, and for that, I am truly sorry. But I'm not sorry I was able to get you out of your clothes. You are a fine looking human."

"You are incorrigible," you say, fighting a grin as you shake your head again.

He grins back at you, unabashed. "Guilty as charged. But the real question is, am I fuckable?"