Help with being toxic

Ok, this board is probably filled with posts like this one but I don't feel like going to read about someone else is going to help me a lot.

In my last game I insulted one of my teammates in the post lobby, as it turns out the one honor I got from that game was from him, it was a very one sided game where everyone was dying over and over, except for me, until the enemy team started grouping and I just could not stay safe anymore, I made several passive agressive comments during the game, but none directed at anyone in particular, not trying to justify myself, just adding context.

I want to stop doing that, because I feel like a piece of shit after insulting a player that thought I did a good job, I apologized to him and he accepted my apology but I don't want to feel like this ever again.

Please if you have some advice as to how I can do it, they are all welcomed I vowed to myself never to do it again, but I don't know if I am capable of doing it, but I really don't want to feel like this ever again, this post is in part to vent, the guy even asked me to play another one after, sadly due to time I can't, but this sentiment of unworthiness its not going away, jesus it wasn't even a ranked game, if anyone read the whole thing, thanks for your time, advice is welcome, and even insults I wont argue.