Guys, do you get jealous/protective over your female friends?

My serving shift ended and I wanted to have a couple drinks at the bar, so I go sit in between my regulars, Mike (26) & Dakota (22), and buy us a round of shots and my drink. I bartend normally, and the bar was busy, so I was happy to take the easy serving shift since I have to work all weekend. So I get the round, stay off my feet for a minute, then I go to talk to my other male friends/regulars, Milo & Troy, since I work in a predominantly male bar. I look back over and see Mike looking at me, and he looks upset. I just smile at him and go back to talking to my friends. I look over again not too long later and the smile that Mike normally wears isn't there and his eyes are narrowed as he goes from looking at Dakota and then to me as he talks.
Later Mike's trying to leave to get me a half and I'm getting another drink, so I stand next to him with a chair between us, and he still looks upset, so I tell him so and I go up behind him and give him a hug, which put a big smile on his face.
I brought it up to Dakota's lady later and Dakota was the one to answer saying "Well, I'm going to tell you, he REALLY appreciates your friendship" and I'm over here like wtf. I talk to everyone, I fucking work there. Mike & I did have sex once, but I don't think that should mean anything, sometimes sex is just sex, and we both agreed to keep the incident to ourselves.
I'm not understanding why the fuck he was looking at me like he was upset. I'm not understanding why he was cold towards me from the time I went over to talk to my other regulars to when I hugged him. I like Mike, he's a good guy, but man...
Any bright ideas? Cause I'm at a loss.
Guys, do you get jealous/protective over your female friends?
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