You've reached the ceiling of your current skill. But not your TOTAL ceiling.
Ask yourself, when was the last time you aim trained for 30min every day for a week? When was the last time you hopped on custom games to practice/find out new stuff for the agents you play? When was the last time you recorded your gameplay and reviewed it?
If you get a KD of 35/14 and lose, what's your reaction? Is it to complain about dropping over 30 kills and still losing? Or is it a winner's mentality: I died 14 times, were all of these deaths necessary? Did I really have the maximum impact I could have every round? Why did I finish 35/14 instead of 35/13, could I really not have avoided a single one of these deaths?
You've reached a plateau (we all do). Now it's time to improve, not to mindlessly play ranked.
Good luck man, if you got to plat you can definitely get to diamond.