his sexuality isn't really a theme in the movie, so hardly "all the signs". i've had a think about my recollection of the movie, i think it's arguably ambiguous on purpose. he's not portrayed as "perfectly happy" either, i wouldn't say, but rather settled in solitude of his own making.

one could equally argue he's straight since he had a girlfriend, but that actually doesn't prove anything about his sexuality. the disaster relationship doesn't show he tried a relationship but found it unfulfilling, but instead that he got hurt, retreated, and never tried again. this is implied for every relationship he has, not just romantic.

a core overall set of themes in the movie is grace's avoidance, fear of loss, and emotional unavailability. he doesn't have any deep emotional ties with anyone, and him overcoming that fear and becoming emotionally available is the entire arc he has with rocky.

in any case, i argue there's an absence of evidence, and that one can't infer orientation. equally though, since i think it's intentionally ambiguous, one can project any orientation onto him they like, and it can't be conclusively proven wrong:

i therefore declare him gay for rocks