In any case, Keith is a person of some kind or another, invented and written by Mutt. He has a strange headspace and forms mild, noninvasive mindbonds to people very easily (sometimes deliberately, sometimes almost accidental), for which his aforementioned strange mind acts as a kind of hub.
Certainly in this stage of his life cycle, and to some extent throughout his life so far, he's one of those people who define themselves by their relationships to other people. In Keith's case this doesn't only mean romantic relationships, though he is given to falling in romantic love with most of his friends extremely easily. He has a huge circle of acquaintances and has had a fair few romantic and/or sexual relationships, though not as many of these as you'd expect. In actual fact, Keith prefers to pair his friends up together - though, again, this isn't only confined to romantic pairings-up.
Keith isn't even his real name. Keith is just what I call anything I haven't named yet. In one planned-but-cancelled storyboard he would have gone by something like Kiko Février.