Is it possible for you to catch diseases from a lil spit getting in your eye?

Yes, but unlikely: Yes, it is possible but unlikely. The spit would have to contain infectious organisms which would have to find purchase. The tears also rinse bacteria and such away. Bacteria landing on the eye usually get bound by antibodies in tears then rinsed through the punctum to the back of the nose, down the throat, to the stomach where strong acid kills them.

Technically, yes.: This is fairly unlikely because the healthy eye has a very effective immunological defense system. Nevertheless, a sufficient innoculum or breakdown in defenses could result in transmission of infection. The surface of the eye is a mucous membrane.