We're not dating, but he gets jealous and possessive when I talk to other guys. Why?

S0ph5t3R
We're good friends and I thought he had liked me since we met. We do lots of things "together" like we bump into each other a lot and end up working out, walking to class, etc together. That happens literally every single day of the week. I started to like him back so I tried to let it show but he seemed to pull away. So I moved on, a bit butthurt cause I felt he led me on and played. I'm now seeing one guy and I started talking to two others. All from our Latin dancing club, which the guy I'm talking about also goes to every week. Every time I was dancing with someone, I had noticed he either was almost always around where I was dancing or always kept an eye on me. Yesterday, particularly, I glanced at him a couple times and he was always looking my way. Every single time I looked (and I looked a lot!). I felt like he was watching me.
On another hand, the day before, I asked him to come with me on an unplanned double-date because I didn't want to be a 3rd wheel (my friend had begged me to come) so I asked him. He accepted right away. So we got there but he went from all happy to see me and be with me to bored out of his mind. So I concluded things were over for good but, the day after, he gets all jealous. No matter what the answer is, he lost his chances and his attitude was a total turnoff and he's not boyfriend material to me anymore. I came to the conclusion that he might like me but not want to date me. And my friend says that he sees me as a "sis" and that he's protective.
What do you think?
We're not dating, but he gets jealous and possessive when I talk to other guys. Why?
2 Opinion