My girlfriend’s coworker buys her food and I feel uneasy about it?

I’m starting to feel weird about my girlfriend’s coworker. She’s been working at her job for a few months and all of a sudden this male coworker starts buying her lunch. He done it for a couple of days so far and my girlfriend tells me all ecstatically. I don’t know what to do about this without coming off as insecure.
My girlfriend’s coworker buys her food and I feel uneasy about it?
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