What am I doing wrong? I was platinum a month ago, then I suddenly started losing, I got to gold 3

Last month I was in platinum 3, I was still carrying most games with great kda, roaming, warding enough, prioritizing objectives, and then I suddenly started losing, I don't want to blame my teammates, I believe the winrate is my fault, not my team's fault. I have great kill participation, great kda, I am getting 5/0 in early, I am taking objectives, but then enemy team gets fed and I am not able to do anything. I keep losing no matter how great I play, it makes me feel sick and hopeless, I literally broke a glass and hurt my hand because of it. Can someone tell me what can I do to start winning games again and get back to platinum?
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