i can ramble on forever! i have no pb preferences but i did have a wild thought that a pb that looks a bit older than him would be fun, in that obviously he's vastly older and that's be a fun little parallel. but ultimately i have no preferences, i'd love whoever you like to play!
as for the line itself, it doesn't have to be romantic or sexual at all, it can barely be platonic. i'm thinking dáire maybe ran into them somehwat recently, just by coincidence - at a store or something? - and that they were maybe being harassed by a super or were being eyed up in a way that didn't look good. dáire honestly isn't the type to interfere in such things, it's not really part of his fae nature, but just luckily for the human he was feeling kind and benevolent and stepped in. since then dáire has been looking out for them and taken them under his wing to teach them about the supernatural world and how to take care of themselves!
i think it could go either way on whether the human likes his attention or not, either they can be adamant that they don't need his help but dáire won't listen, or they're thankful that he's looking out for them and they can become friends! though also there's always the possibility that down the road dáire will decide that he's going to cash in his kindness for a favor because, y'know, fae.