Teekaymon
I heard Sensui cared for him back. *shrugs* I dunno where I read it, but apparently he was a homosexual.
I like Itsuki x Sensui simply because they exist. Itsuki accepts and loves every aspect of Sensui - and admits that it's Shinobu though, that he loves most. He follows him, knowing Sensui has every intention of allowing him to die - but they were obviously incredibly close.
I don't necessarily think it was one sided, as much as it was just never explored in full on Sensui's part.
I dunno whether I got the impression that Itsuki was in any real danger. He's a very powerful demon in his own right, and can hide in complex and impenetrable ways. I think he follows Sensui devotedly, but that there's not necessarily any tacit acceptance that Sensui will let him die, because just opening the tunnel wouldn't have posed that much of a danger to him.
(I get the feeling that I've managed to miss something, but I
just watched the arc in Japanese, and I didn't get that vibe.)