This answer contains spoilers… (view spoiler)[Agreed (with Hannah). From the sounds of it, Fae seem to have just one mate and Rowan lost his. I could of course be wrong about them being monogamous, but it is definitely more of an eternal gratitude and respect for someone who has become his friend when he didn't think he deserved one. Celaena even thinks about sleeping with him but it wouldn't be right, and how she kind of hoped she had feelings for him but she didn't have anything but friendship. (hide spoiler)]
Hannah Cook I think they're just friends. They're distantly related (he's Maeve's "nephew of sorts") and Rowan's still mourning his mate (I forgot her name). I really hope they don't get into a romantic relationship!