All good advice, though I'll definitely push against point #3 from Juice. While you'll invariably become better over time piloting one sort of deck, branching out into other sorts will yield a surprising amount of value. For example if you tend to play control and branch out into aggro, you might notice certain play patterns you can exploit later when you play against aggro the next time. Particularly relevant to EDH, if you try out combo even though its not your thing you'll quickly realize which cards are important to interact with and when.
Since you've done the legwork of narrowing down what the issue is, allow me to just say it: He's probably just a much better player.
What you're feeling is frustration at being outplayed, and there's only two real courses of action available to you. Do you...
A) Get angry and allow it to make you bitter, or...
B) Strive to improve so that you can compete with him.
My advice to you is to spend more time watching him when you're playing, and if something seems peculiar or deliberate and you don't understand why he's doing it, just ask. Most good players are more than happy to explain their thought process and play patterns. Chances are, he's just better at sequencing to maximize his mana, or has better threat assessment and as such doesn't waste cards when he doesn't need to, or hell maybe he's just subtly politicking his way through games and you're not catching it.
Whatever the case, the best thing you can do is figure out why you're losing and attack it instead of worrying about how it makes you feel. Don't address the symptoms, address the cause.