idk if you're still stuck to this day but here how you get it
SPOILER
: on her first date assume she has familly issue, apologize to her, stay silent. on her second date: say you're sorry or hug her.
the way the game works is that each good choice add's a +1 love point when enough love point you get the good ending but for Miyah's you need SPECIFICLY 4 love point and asking her if she walks around here on the first date adds a point so you need to take one wrong option or else you'll be at 5 point which triggers the bad ending