Middle of top lip keeps splitting. i stay very hydrated and have used different types of lip balms and nothing is helping. could a vitamin deficiency cause this?

Cheilosis (cracked lip) often occurs at the mouth corner and it may be caused by vitamin B deficiency, especially B2 (riboflavin) but you have problem with upper lip at the middle and not improved with lip balms. There is no harm if you want to try vitamin B complex for a couple weeks as a trial. Cover your lips with a scarf when going out in cold weather, don't lick and avoid favored lip balms.