Play with maximum comfort - All in PACK
I killed this little worm ;) because it stood on my way to win. I had more chances to win alone 1v3. He would probably missclick and kill my army with tanks or steal my precious minerals, so I decided to avoid that. That resulted in good 1vs3 game and in the end my win, as I predicted. I can provide with replay and then you will understand the game.
We have already watched the replay.
Your ally didn't deserve that treatment so you are in total fail and even if he did deserve, backstab is one of the most hated behaviors and it's forbidden by the rules.
7. Fair Play
In team games it's forbidden to change the allied settings of the current team. If a player unally his current team mate in a 2v2 game and/or ally with the opposing team, the game itself will be delete; Punishment: clearstats + lockacct
The decision stays.