I'm not sure that I'd take anything that Jaehyo says about Zico's sexuality too seriously, seeing as how he was saying it as a joke when Zico tried to kiss his neck. Jaehyo was also the one that the others said wasn't comfortable with having male friends...
For reference of anyone else, the scene I'm talking about is in this video near the end.
Anon, that's a fair point to bring up and I am aware of the context of his statement but even if it was a complete joke, I don't really think it contradicts my overall opinion on Zico's sexuality at all to be honest. There's a lot to that little scene that can be analyzed beyond just saying that Jaehyo's statement was a joke and doesn't mean anything.
If you've ever heard someone say that every joke has a little bit of truth to it, I think that applies here. Why was Jaehyo joking about Zico's sexuality in the first place? The obvious answer is that Zico kissed his neck. Even then, he could've just said something along the lines of "Why are you doing this?" or "That's weird" or something, but he mentioned Zico's sexuality. It could mean nothing, but it could also mean that Jaehyo either knows or suspects that Zico isn't straight and that came out in his response as a joke.
Besides that, consider the context of the joke: Zico randomly kissed Jaehyo. It might not mean anything, but honestly, most guys I've known who play around like that (being overly affectionate to other men) are doing it as a "joke" because they're confused about their sexuality and don't know any way to express or deal with it except jokingly. And the fact that Zico switches between playing around with kissing his band mates and looking really uncomfortable sometimes at being overly touchy with his band mates does nothing but make me think that he's queer even more.
You can also consider Zico's reaction. When Block B was joking about Taeil wanting to kiss Zico on World Camp, Zico was cracking up and didn't seem uncomfortable at all. After Jaehyo's comment, Zico just stood there-smiling but not really laughing. It's obviously open to interpretation but I think he looked vaguely uncomfortable. This could be because his sexuality was being brought up on camera or because Jaehyo seems more uncomfortable with male affection than the other band members, which could potentially correspond to him not being as comfortable with the idea of a non-straight band member (this might be unlikely, as it seems like they've established or joked about Taeil being gay, but we couldn't see Jaehyo's reaction to that on World Camp, so who knows?).
The point is, if his sexuality weren't a sensitive subject, I might have expected Zico to react a little differently; if he were straight and comfortable with that, then he might have found it funnier because the idea of him not being straight is so ridiculous. But it seemed to me like he was kind of trying not to react, if that makes sense?
Obviously this is a lot of analysis of a very short scene, and it's all pure speculation on my part. But my point is that just because it was a joke doesn't mean that the story ends there.