Ok so this is why i think the author made maythan warm up to the lil villain prince real fast.
Maythan's actually running on whatever knowledge he has from the game he played the second half of. He knows he's a "bad guy" in the story and tries everything to distance himself from the main characters so he can avoid his fate. To top it all off, all the male leads not only wanna hang out with him, they wanna bang him!!! He probs decided to hang out with Ian coz a) anyone who calls you 'bro' obviously does NOT wanna bang you, so that's nice, and b) Ian probably was a shadow figure in the game so Maythan doesn't know that this guy is the worst of the bunch.