Jealousy and admiration are two sides of the same coin, it's just that in this case it's gone a little too far. Male best friends are always in a slight competition and it's no surprise that you've lost for the entire duration of the friendship.
Now that loserhood has blossomed into an erection. Looking at how strong he is compared to you, how hot he is, how many bitches he gets? It no longer pisses you off, it makes you horny. There was no chance of you ever being better than him so of course you had to sexualize it to feel better.
Follow directions and let that goon brain do its thing. All the porn you watch feels like nothing when you get to finally embrace who really turns you on.