Painfully Jealous

E.
How do you all cope with being jealous? I'm not really jealous of other girls in real life, like friends of his, but it's online girls that I'm super jealous of? For example, he follows Jessica Nigri on twitter and I'm sure YouTube. That girl is literally famous for having big boobs (and cosplays okay okay but we know what guys are there for, especially my guy who really isn't interested in that kinda thing at all). It really hurts me for some reason when I see him following these hot girls online (many of which are gamers because he games a bit... and I'm terrible at video games) and I don't know why. I just don't like that he looks at other girls in most likely a sexual way, ya know? I don't want to be controlling and tell him to stop, I just wanna know how to stop being so jealous!! The other day I literally got upset because he jokingly checked out a character in Overwatch's butt :-// I'm too sensitive and I know that I gotta chill, but man it sucks. 
Part 2: This was originally just going to be a post about jealously over other girls but I'm jealous of his friends too... I never thought I'd be like this but here we are. He plays video games with his friends a lot and if I try to text him during that he kinda ignores me, and I know for a fact he likes me less than he likes his friends. He calls me his best friend, and I 100% consider him my best friend, but like... every time he's with his other friends I'm SOOOO jealous!! It's so bad. How do I get over this??? 
Sorry this is so long, I've just got a lotta emotions and need help!! Thanks buds