I doubt you are playing any differently than usual. I don't think you had an easy win available at move 18. You did make some errors to lose the game but I wouldn't call the moves "retarded".
You state there is no point in doing tactics yet it seems that your peak rating came after a period in early 2015 where you made a large effort to do tactics.
The biggest tactic you missed was on move 21. 21. Nxd6 is precisely the kind of move you need to find in solving many tactics problems.
I played the following game: