From my experience, knowing that when I was younger that I was much the same, I can relate to an extent with you.
I was terrible about wanting to 'always win' in games, to the point where in things like Lemmings for example, i'd undermine the spawnpoint and have a pixels difference in the size of the bridge covering it.
End result?
The person I was playing with's lemming fell past the bridge and mine fell atop it.
When you resort to doing things like that when skill fails you in games as you have to win at any cost, people quickly stop wanting to play with you, so I found myself shifting my perspective.
The most important aspect of the game is fun, and sure, while winning might be 'fun', it's a very superficial kind of fun where you enjoy a feeling of superiority at the expense of the other(s). Sure, I'd get frustrated when I faced impossible odds in games as well, when nothing I could try and do would overcome the challenges.
While I was looking to change my perspective on things, I found roguelikes.
Suddenly, I was dying again and again and again while still trying to learn how best to play the games - and still approaching them head on like many of the games i'd played before.
Around the same time, one of my brothers started to take a more active interest in gaming, though, he didn't want to directly face me as he was afraid of losing.
He also didn't want to face higher than easy difficulty alone on games without me to 'save him'.
In order to continue having somebody to game with regularly, I had was required to protect somebody who would have been considered by any other to be deadweight to the team due to lack of experience and skill, who I realised wasn't going to have fun - just like with myself - unless they were winning.
As things progressed, he went from deadweight who was more of a liability to me, to somebody fully capable of watching my back when I was leading the way in games - thus endangering myself on his behalf, as we'd progressively push the difficulty settings higher until we had to be very careful.
We went from trying to grab the best gear for ourselves, to splitting it based upon preference and role - while he still defers to me and would give me the best protective gear if I requested it, that's because typically he expects me to go into new situations first and if that goes badly, for attention to be off him long enough for him to run to my side and save me.
Sure, we get bored, we backstab each other, we try and force each other to spawn over bottomless cliffs or whatever.
In short, I was underhanded and competative to the point nobody wanted to play with me, I learned to distance myself from the game so that repeated deaths bore me instead of frustrate me. My brother needed somebody to teach him the ropes, I took that challenge up and taught him to be as underhanded and merciless as me, while at the same time teaching him not to get frustrated when things went wrong and got him killed.
At the end of the day we're all human, but this is my experience with things. I have gone from competative to more content to teach and explore, though no less of a bastard for it.
The catalyst for that change was having a brother who needed a hand learning how to play games who I could see something of myself in, that helped me mature somewhat (contrary to my handle on this forums. I should really get that changed...) myself.
Changing because you want to change takes a lot of self control and willpower, changing with a catalyst of sorts to assist makes things go a lot smoother.
Hopefully my inane rambling is of some assistance in this matter.