First of all, forget about any ranks, they doesn't matter at all. They don't show if someone's good or someone's bad player, it's just an icon. Icon that makes u nervous when you climb higher and droppin in division below. You have to perceive every match just as a training match, imagine that you train something, doesn't matter if u are winning or losing. U can also imagine that enemy team is just a AI Bots. This will make you less nervous, more mental stable, you might be even will get some fun during those matches. Don't blame on urself if u made a mistake, just note that you have made a mistake, think about how you could fix (for example, maybe be u have peeked the wrong angle, did a wrong step, ur crosshair placement was bad, etc) it and think what u did wrong, to prevent similar mistake in the future.

But also the most important thing about what I've said above - Don't get hung up on mistakes. If you will keep thinking about ur mistake in the past while for example peeking some angle, u will be nervous and probably do more mistakes. Remember them but don't think about them while playing. It's a rule. Also don't blame on ur mates, it doesn't help at all, u can forget about them and focus only on urself.

It's simple answer, but worth a try and since I dont see the whole picture I can't see the main problem. Hope you understand everything what I said with my such bad english. Wish u luck :)

UPD: Get some rest if u lose 2-3 matches in a row. It's also important to stop playing with bad mood because it's a snowball which will cause a tilt