It also depends why the guy doesn’t want to label himself – there’s a big difference between eschewing norms as a form of self-expression and hiding who you are to manipulate the advantages available to you as a straight person. The straight guy is worried his “secret” will be uncovered while the gay or bi guy fears he’s being used or unworthy of a relationship in public view. Clandestine relationships or regular hookups with one straight and one gay/bi guy sometimes exist in a mutual state of insecurity and fear.
It depends how things play out, whether it’s out in the open or “our little secret”. But what does it mean for those guys who do embrace their label but have sex with guys who don’t? Does it mean their lovers are any less available to them because they won’t pick a side? Of course, nobody needs a label, but for gay and bi guys who worked hard to establish their identity, how does it feel when the man they’re sleeping with won’t do the same? If you’re a man who has sex with men on occasion, but identify as straight, who’s to stop you? You are who you are.