Along with Saitama, he is the person Genos most loves and admires because of his intelligence and help, and has gone as far as standing up for Saitama because the latter called him "old man", though he later apologized for his attitude after Saitama told him to not take it so seriously.

Does Saitama cares about Genos?

Saitama holds some respect for Genos since he became an S-Class hero right off the bat, and desires to move up the ranks due to his S-Class status. Genos has become Saitama's companion and friend (or at least close to it).

Is Genos jealous of Saitama?

And Genos is an extremely detail oriented person. He's the more likely to get Jealous compared to Saitama. ... But mainly, his jealous asserts itself through dominance displays and possessiveness.