Sorry I don’t remember too much but I just thought it was annoying bc FL liked him in high school. The translation calls him her ex but they didn’t seem to date, since as far as I read he was nonchalant to her. And then he supposedly likes her but he let 10 whole years go by before the blind date so to me he doesn’t seem to like her that much…
I forgot which chapter it was where the ML's friend mentioned that MC went somewhere and ML was surprised to learn about that since he tried to contact her before but was unable to, so ML realized that it must be that reason why he can't find her.
MC liked ML first but ML eventually fell in love with MC. There should have been a misunderstanding between them before like when ML said to MC "never look for me again" something similar to that statement, which is why MC went somewhere ML can't reach her (this is my opinion only not a spoiler)
As for EX thing.. MC wrote a webnovel where the settings was about them being ex lover when they are not in reality.

ML gets on my nerves. He hasn’t done anything but he’s just so smug, you know? I want the FL to make him sweat a little.