Your post isn't making any sense, did you invite him to the game? If so you are the fireteam leader, he can't boot you, did he invite you from lfg to join? If so, it's his fireteam and unfortunately he can kick you if he so chooses
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I was fireteam leader ended up promoting him because of his "lag" obviously yes I made a mistake for giving him the ability to be able to but not an excuse for his thieving actions.
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Here is quick bit of advice for you, making somebody fireteam leader does not change the host of the game therefore does not affect the lag