You must find wherever the BFF is, they can pretty much be anywhere at the daytime but at the night you can pretty much know where they are if you press their nightlife schedule and after finding wherever the BFF is press the "People" and find wherever the BFF is in the list of "People here" after that go talk to them and change your relationship to poly although you need the polyamorous inclination for that luckily cheats are there to help just don't put a space in the end since it won't grant said inclination and if you don't know where cheats are I think they are in the difficulty option setting and scroll to the down then turn on cheats luckily there are no consequences for turning on cheats so yeah oh and don't ask them out on dates since that won't work or go to their room you Must talk to them in person to change said relationship oh and you also need I think? Maxed out romance for them to agree into being in poly relationship with you idk about lust and friendship though but yeah hope that helps I guess