
Not to be disrespectful, but they probably asks that because the person had dated only girls and now they dates a boy without coming out as a BI. Or the person never came out of the closet or it’s their first time dating their same gender when they were dating their different gender before. ٩(๑❛ᴗ❛๑)۶

I don't think they mean any harm w it. (at least not the characters in this yaoi here) It's more about quenching their curiosity. I'd really count that as questions most would ask when someone enters a relationship. Humans are born with curiosity and I think it's just something u'd want to know. Me for example was the same when a friend told me they were gay. I was just like ' oh really? Like did u always date the same gender or also the opposite? Or how is it now? Or who are u w now?' It's not meant to offend someone but naturally u'd want to know more about something ur not familiar with and I think it's a great thing if u can just talk about it because like that I for example got a small insight into a topic I'm not familiar with and later on I could respond in more appropriate ways because I then already had that knowledge and all. Of course some questions u ask are sometimes not the best but as long as the person in front of u knows or u show them that u don't mean any harm by this I think there is nothing bad about that. How should people know about something they haven't experienced themselves before?
why does everyone in bl’s ask the main character “oh since when have you been gay” like ? you don’t just suddenly become gay you’re born with that bud