Well then it was your fault for being out of position and making it easy for nasus to catch you. Next time stay with your team and either kill nasus before your team contests an objective or CC chain nasus so he can’t do anything in the fight.
Fighting a fed nasus or mid game (not fed) nasus will be far easier if you, as the squishy champ, doesn’t try to fight him alone. If you are having trouble with the nasus slow, buy a
in the beginning of the mid game phase. ask your support to go tahm and stay with him when you try to fight nasus, that way tahm can eat you and get you to safety when yo are slowed and he isn’t, but if tahm is slowed you have your MS ability the MS boost from heal and flash to still get away.
What I am saying is to never fight nasus in a 1v1 scenario if you are the squishy ADC or APC. The only exception to this is if you are a fed Vayne. Vayne shreds nasus hard with bork and rageblade, and her q during her ult makes her go invisibl, which makes it harder for nasus to Q her. And she does have her e to easily kite the nasus if he wastes flash or ghost to try and engage on the Vayne.