what rekt you isnt probably the counteritemizaton options but the way your build evolved
if he won early and got some gold you cant simply build yourself up like you do it every game
he started to build based on what his enemy does while you were prolly just adding up the stuff that he already counntered
if yyou play a guy like darius vs teemo you need to know what teemo hates and counteritemize it
also asses your kill potential ... if oyu can kill him carefully do it but if you cant dont let him take kills to not get counterbuilded into infinity
i played loads of games with my friend who is realy good at 1v1 games
we played on aram and he always died first yet then he always counterbuilded me into infinity and i always lost