What made him say this?

I have a crush on one of my guy friend’s friend. I used to be friends with this guy but all of a sudden my guy friend doesn't talk to me as much and when he does, he's asking where my crush is. I had a feeling my guy friend liked me but he has a girlfriend.
Today me and my crush were hanging out and he left to do something. My guy friend comes to me and asked "where did your boyfriend?" I was so confused. No one knows I have a crush on him. Before, I did talk to my crush a lot when all three of was hanging out together but nothing flirty.
What made him say this?
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