Listen to my story: I'm tired of losing and I need help to improve!

Hello everyone;
Please, listen to* my story:

I’m a big fan of Fighting Games, specially KOF and XIII is my favourite KOF ever. But I’m not as good as I wanted to be.
You see, I got some “skills”. I managed to complete all the 10 trials for Kyo, EX Kyo, Elisabeth, Leona, Ralf and Mai. If only execution were everything…
I have watched every single video from Juicebox about KOF XIII and that helped a lot; I have watched a lot of pro players matches to see how they understand and use the fundamentals of the game and I’m trying my best to improve, but I’m still not seeing progress. :s
You see, my main team is: EX Kyo, Leona and Elisabeth and I won’t change to EX Iori, Mr. Karate and Kim. In fact, I don’t think the problem is lying on the characters area, but it’s lying on me. If I can’t win consistently using my main team, neither will I do with the “EVO Team”… I believe.

The game is basically dead now, therefore I only know a few people who still play the game on Steam. To be more precisely, when I started the game I met this guy playing online around one year ago and he was a waaaaaaaaay better than me; he’d kick my ass every time -and I mean every time. Nowadays, I’m better than he is, I won almost every set we played on the past days. Now he gave up on playing against me, claiming that I have bested him. I took that as a compliment.
Obviously, as the time would pass, we would improve and things happened just like so; the way we played the game one year ago is very different from what we play nowadays, that’s obvious. I just want to point that to say: it seems I have improved faster than he did, since I started way worse than him and now I’m better.

Well, then I met another guy this year playing online and guess what!? He’s waaaaaaaaaaay better than I am. The score of our last set was 54-3; and man, am I frustrated! That’s shameful, but I want to overcome this, I want to become better, but the thing is that I don’t know where I’m making mistakes, what I do know is that everything I do gets beaten. If I think to hop, I get rekt by his air to air, if I full jump, I eat an anti-air, if I try to run, just so I can mix up my “aggression”, I swallow a normal of some sort… it seems he’s in my mind. Man, I’m lost in this game, I don’t know how to make him scared of pressing a button, confused with my mix ups or make him sit on the corner; instead, I’m the one scared to press a button, I’m the one confused with his mix ups and I’m the one sitting on the corner.
I don’t know what to do to become better, despite having the will to do so.
I need your help, guys. Please. I’m frustrated and tired.
Thanks. :s