The only reason I can think of is that its viewed as feminine and men don't want to be seen that way so they don't use it. Because its viewed this way women wouldn't like it either. There may be some individuals who feel differently, I'm not generalizing just saying my best guess lol.
I seldom wear any because of the hassle of putting it on, so I can't imagine why any guy would want to for any reason go through the trouble of putting on make up, with a costume party being the exception
i don't think its gay, if a man wears full makeup with lipstick and eyeshadow he might be a tranny or a drag queen. But when I see a guy with eyeline or an example I think he is a glam rocker or just a rocker
only korean popstar singers use make up when they sing, unless your one of those or an actor or going to the premiere of a big Hollywood blockbuster like Star Wars 7: the return of Skywalker. I suggest you leave the make up to your girlfriend, if you do not wanna be labeled.