@Tcof:
The fujoshi spirit in my soul would like to suggest the real possibility that he's bi, got hit hard when
someone got a girlfriend and, on the rebound, picked up a nice girl with a mean look as a replacement-goldfish for the protagonist.
But realistically, I think he's supposed to be just a clingy guy all around, with people who become important to him.
(Either way, we already know he's gone out with girls before, from remarks in previous chapters. If he's straight-up gay, then he's deep in the closet and in a really unfortunate position. But, again, that seems unlikely to me.)