How can I find out if a guy I'm dating has lied about me?

Been dating a guy at work. We haven't slept together, but something he said made me believe he's lied and told a couple of people in work we've slept together. He seemed to slip up. I asked if he had said it, but he said he hadn't told anyone that. So I let it go

But the people who I thought he'd said it to have started acting different towards me

Is there anything I can do or say to find out if he's lied, without directly asking the people I think he's lied to?
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How can I find out if a guy I'm dating has lied about me?
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