Why does a guy I’m friends with but has a girlfriend talk about me to others?

We’ve worked together and always gotten along but it’s been platonic. It wasn’t until a few months ago, after 2 years of knowing each other, he started acting like he had an interest. I don’t really go along with it since he has a girlfriend. Anyways, In the last few months he’s told me he’s talked about me to his mom, cousin, co workers, and even girlfriend. I don’t know how I came up with her all
He told me is she said she’s worried he’s gonna leave her for me, and asked what I thought about that. Anyways, I know his cousin and he has in fact told me he’s talked about me and I’ve had another co worker confirm he talks about me. They’ve both said he just talks about things I’ve said or asked what they think about me. I don’t get why he would seem so interested in me while having a girlfriend
Why does a guy I’m friends with but has a girlfriend talk about me to others?
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