What does it mean when a guy jokes that you've received a love letter, and then pretends to read it out?

I received a handwritten letter from a client at work relating to support we're giving him. A coworker I'm friends with joked I had received a love letter, and started "quoting it" with all the reasons the client loves me. He went into quite a bit of detail, and looked at me the whole time, I laughed it off but couldn't hold eye contact with him.

What does it mean when a guy jokes that you've received a love letter, and then pretends to read it out?
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