What does this kind of behavior indicate?

I have a close guy friend online who I’ve known for about 2 years. He’s my biggest supporter, and I see him as a mentor. After I met this guy, he and my boyfriend added each other right away. While my friend has always paid close attention to what I do and has constantly given me praise, he doesn’t do the same for my boyfriend despite him trying to be friends. When my boyfriend messages him and tries to get a conversation going, my friend isn’t rude, but always keeps it brief and never seems to want to deepen the relationship. He watches my boyfriend’s stories but rarely likes anything he posts, however always shows a lot of enthusiasm about mine. Because of this contrast, my boyfriend has always been suspicious this guy likes me and it’s a jealousy thing. I’ve considered this a possibility, but my friend has never crossed any lines and I assumed maybe he just doesn’t relate to my boyfriend. Anyways, now my friend is dating someone. Recently my boyfriend attempted once more to start a conversation with him, and was yet again received the same way he always is. Why would this most likely be?

What does this kind of behavior indicate?
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