Sponge Cave Spelunking
Sorin doesn't question how difficult it is to buy gifts for Krelian. Sorin, because he's basic and predictable, likes Minigears. Anybody can hand him one for any reason (bought it especial, or wanted to get rid of it) and he'll accept it gladly, painting over it if it's a model and color scheme he already has.
But Krelian, because they're mysterious and long-lived and philosophical, doesn't go for your run-of-the-mill human things. Books? Plants? Trinkets? Even food is something they indulge in only blithely, blandly. It's like (it's likely) they don't want to think about their continued existence in the world, and instead of turning to material, perishable, short-term things, he just passes from day to day, amassing more knowledge and experience toward no goal or end.
That's Sorin. A nebulous, organic experience. One that Krelian can absorb gradually or in rushes, depending how each day takes them.
But they're always spending time together, and even if Sorin were a little more conceited, enough to consider his presence anything like a gift, there's no way he can pass that off as a confession (a concession) of his feelings and appreciation.
Maybe a conscious shift in the way he approaches Krelian? To give them a little more physical openness, to put more effort into emotional conversations? All too much work for Sorin, who's never stayed around quite that way.
He'll just have to keep thinking.