I always thought that he was gay since the first season of Hawaii 5-0 which to me seems like a very homoerotic show from numerous scenes with him and McGarrett. It's mostly Scott Caan now who's always checking him out up and down; check the first episode of this season at the beginning, McGarrett is changing his shirt and Caan can't keep his eyes from gazing down. So typical of him.
Mainly in past seasons I've noticed in their verbal exchanges there is a lot of questionable or homoerotic undertones that just make me wide-mouthed or laugh even. They definetely know what they're doing, happens all the time. I hope they keep it going this season.