why? what difference would it make if he were gay
Well, I'd appreciate a hypothetical situation with him being a gay person for several reasons: 1. In the case I'd still have an insignificant chance (=0,0000000000001%) of dating him and it might inspire me somehow. Now, knowing he's not gay or bi i have 0% and that's sad. 2. Some gay people are quite open about sending their nudes to their lovers and in this case one day we could get a real nude pic of Nathan in here, but since he has a gf we won't see any real nudes and will still fantasize. 3. It's just pleasant to know that someone who you admire or respect belongs to the same social group (maybe it's even written somewhere in sociology).
But all of this is just an answer to your question. I'm fine with his sexuality and still appreciate him for being that hot positive dude on Instagram.