A straight guy who likes to hang around gay guys = stray guy. Sometimes a closet case, but not necessarily so. Possibly bisexual. Often, truly heterosexual.
Brett is a total fag stag. He likes not having competition for all the women at the party. He's not gay, he's stray.
A person who has recently left someone or has been recently left by someone and is waiting to get asked out, rather than going to find a partner on their own.
Guy #1: Hey, are you still with whats her name?
Guy #2: Nah man she broke up with me, so right now, I'm just a stray.
Guy #1: oh same