Its not worth getting upset over WC3. Believe me I've been there. There are people on battle-net there who just seem to be hard-wired into their computers. They are virtually, they'll probably spend about 18 hours a day playing. I don't have the time or the will to do that. I have my job, wife, house and other things to worry about. Amongst other things.
If you really want to improve yourself check out the tactics websites, play a bit of single-player and use the same hero all the time. Get to know their limitations, hot keys, when and where to use their powers. Just diving into multi-player team games will get you shouted at if you wander around like a noob and haven't practiced. Hell, I'd shout at you. (In a helpful way) Just be prepared.
In the end, it ain't worth it. There will always be someone better than you. They're usually in your game too. <img src="/ubbthreads/images/graemlins/rolleyes.gif" alt="" />
The thing with b-net, the defining motif as it were, is that its ripe with a-holes. Full of them. I find my bored attempts to re-establish my D2 accounts to be the same way now. Every game is full of elitists wandering around with all the gear they traded for hacked/duped runes. Maybe if I spent more time there I could become one too but I don't think I want that... Well maybe. <img src="/ubbthreads/images/graemlins/evilgrin1.gif" alt="" />
One last thing, I hated being 17, you lose a lot of your childhood friends. When you go to university it gets better though. You are going to university right? You seem to be quite intelligent.
Good luck, don't let it get you down.