I think Kyungsoo dated that girl and then broke up when he became a trainee in his third year of high school because things got too hectic. Then he started dating Jongin. Even if Kyungsoo is gay, it's normal for him to have wanted to try and see if he likes girls or not. A lot of people who are gay date the opposite gender for a while before realizing that they're into the same sex
ummmmmm I guess I just really don’t....see kyungsoo ever being involved with a girl in any capacity, like I think he’s pretty much known he was gay from the jump, but there’s no real way to know if you’re right or not
but uhh @1kadi knows more about this than I do (she’s a ksoo stan, I am but a mere jongin stan and know more about him predebut than anybody else) so she might have a better response to this