Just because he was shown first and shown more often in the beginning doesn't mean he is automatically ML. We see this in "When the Villainess Loves" where 2nd MLs were introduced first, and the true ML is shown 40+ chapters into the manhwa. It's normal for readers to be unsure who the ML is, especially since this work has no source material. That being said, no one can really be "sure" who the ML is until they actually end up together because, again, there is no novel for this. Our opinions are all just that, opinions and wishful thinking.