He calls me sister but his behavior and how he treats me is confusing?

I have a close guy friend whom I hang out with and we talk a lot. He would say things like “i’ll always make time for you because i like you (as a friend)” and we hang out quite a bit. He’s very caring and takes care of me but recently he started saying “this sis” or “thank you sister.” I also use bro/dude a lot but i am not sure when a guy says sister, it means he is friendzoning you. What i’m confused is he would go down the length to make time to see me and the first guy that doesn’t say “i’m too busy” or ignores my request to hang out. He likes hanging with me so much that last year during Thanksgiving holiday he asked what i was doing and joined me and my family to our short road trip. by the way, this guy is super popular and has many friends so he has many people to have hanged out with during that holiday. And of course, he also asks me to hang out. Does my guy friend really see me as a sister?

He calls me sister but his behavior and how he treats me is confusing?
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