What does it mean when a guy friend constantly tries to define the relationship?

Does he think I secretly like him or something? I have a guy friend who I was close to a few years ago. When drunk or feeling good, he would say things like 'I can see us getting married or being best friends down the line' or 'this is how our future children would be'. Well nothing happened, he started talking about other random girls to me (then start jokingly accusing me of being jealous) and we drifted apart.

We still kept in contact but not as much as before (say once a month) and that's when he switched his tone to comparing me to his sister (he doesn't have any real sisters). Again he kept defining us without me asking or even flirting. Instead he would send cheesy love songs to me randomly then tell his friends that I am like a sister so they better not flirt with me.

Now he shifted again. He would compliment me ("You're lookin' smokin'!") I would say thank you then drop the subject. It's a compliment, nothing more than that. But then he'd be like "I love our new relationship. I'm like your gay best friend!" New relationship? Gay best friend? Wha? And when I asked about his friend, he asked if I was interested. I said 'why? jealous?', I was teasing since that's how he teased me about those previous girls. He replied with 'Hardly. I have someone'. But...I was just teasing! Like he did! Why take it so serious?!

So I'm confused. Why would a guy keep defining our relationship? Its not like I am constantly messaging him or flirting with him; in fact he is the one who would send me random 80s love songs or text me that I'm looking good. I don't get it. Any idea?

What does it mean when a guy friend constantly tries to define the relationship?
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