How does Di feel about Deo kissing other people? Even in a non-romantic way?
Well, romantic or otherwise, it isn’t something Diederik enjoys thinking about, you know? They know it’s greedy of themself, so they curb the feeling as best they can, but they can get a bit jealous when they see it or hear someone else mention getting a smooch or two from Deo. They can usually curb the feeling just fine, but it gets quite difficult when their soul gem is dark (which proposes the question: does it get dark because they’re jealous easy or do they get jealous easy because it’s dark? maybe a bit of both?)
Their main problem is that they have never loved (or even lusted after, never even had a crush on) anyone other that Deonte. They were very firmly demi, both romantically and sexually, and even since meeting Deo no one else has caught their eye. Deo, on the other hand, has dated at least one other person (Natalie, who Diederik is actually decent friends with), so there’s always the slight fear that.... well, what if those platonic smooches someday aren’t platonic anymore? What if Deonte moves on? He’s liked people before Diederik so who’s to say he won’t like other people more later on?
It isn’t a healthy fear to have so they don’t bring it up. Deonte is his own person and the last thing Diederik would ever do is stop him from doing something he’s simply know to do. It’s how he expresses his caring side with people and Di knows that Deo has a hard enough time figuring out how to deal with that, as it is - so they don’t complain, or even bring it up at all.
Basically.... They don’t think about it. They don’t want to think about it. They won’t stop him, but thinking about it hurts.