Boyfriend doesn’t flush after peeing

Why is it so hard for someone to flush right after using the bathroom...? I’ve asked plenty of times nicely to FLUSH THE TOILET... am I overreacting...? No matter how nicely I say it, he always tells me it’s not a big deal. But it is to me 😭 and I’m just asking for him to be considerate. I mean, Is it wrong for me to not want MY apartment bathroom to smell like piss that’s been sitting there for hours. I don’t even feel like I should have to tell him to flush after peeing