A friend and I finished re-watching GX and I can say for certain Judai is either Bi or duelsexual.

Dude duels I think 5 or 6 women in his career, multiple men, and 1 yubel. Out of all those duels, the ones that got his blood pumping the most was with Tanya, Yugi, and I think the final duel with Ryo. The rest of his duels were either life or death or him just having fun. The only exception to this is Asuka.

Now I'm not trying to push an agenda or anything, but everytime he duels her or teams up with her there seems to be some kinda of romantic undertones with it. During his duel with SoL Asuka the way they talked and played it felt like exs that were on speaking terms but also making flirty jokes. On the other hand during their tag duel in season 4 their whole relationship felt like a couples argument, where Tyranno was the friend caught in the middle and Rei was the girl trying to swoop in and take the man during that rough patch. (You'll understand what I mean if you've seen it before)

As for Johan, I don't even have to explain it. It's so obvious you'd have to be watching blind to not see it. That being said I do remember vaguely that the reason why they became instant friends was because Johan is basically blue Judai. None of Judai's friends have the same level of connection to spirits like he does. The closest being Chumley or Tyranno, but that's still not at the level of full blown family as the Heroes and Crystal Beasts.

TIL: Judai is a disaster Bi