Partner had sex with another man, but says he's not gay

So my current partner told me he had sex with another guy a couple years ago, before he and I. Said he was using heavy drugs at the time…and blames it on the drug use.
He’s really masculine and great in bed with me so I’m unsure what to think. Why use and have sex with another guy? Why not a woman? Can drugs make you do these things? Help!!

He could have just been testing the waters. Does not make him gay. Everyone tries things.

I’ve seen people do all sorts of things outside their normal while on drugs. Absolutely doesn’t mean he’s gay. Drugs completely alter how you act in situations.