How do I treat him after he used me?

I assume a coworker used me for either 1. my body or 2. an ego boost - or both, considering he stopped pursuing me after I rejected sleeping with him. He's in my group of friends at work and we eat lunch together. He's also in my department but we don't work together often, if ever. How should I treat him? Do I ignore him? I still like him. Sucks.
How do I treat him after he used me?
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