Definitely bisexual. Leaning more towards straight than gay though. Sorta like the guy that would start making out with someone if provoked correctly but would never dare initializing it because of insecurities. Just needs a nudge to open up that little closet of his. His attraction to Naoto is a sign of this, he liked her before knowing she was a chick and liked her after knowing she is a chick. A couple of my friends are like that, would happily live their lives as straight men but wouldn't be all grossed out if "things" were to happen.
If this was a bioware game he would definitely be the boylove option.