It could also be that Lily still has no problem with a threesome, as long as she doesn't count them as close friends and there isn't a likely chance on a relationship.
I actually think she will leave the Pink Rose for him, she's found someone that accepts her as she is and she's not used to that but she loves it
Josy still holds a candle that doesn't seem to be fading but instead getting even more intense, Josy would be more the issue here
Lily was ok with it because it was with Nicole and they weren't rolling at the time of the Halloween 3some, but in 11 you have to make a choice between Lily or Nicole from now on, once feelings get involved, which have now happened it gets complicated
This is of course all just speculation but from what I can see it STILL feels like Lily has been putting on an act all this time, now she knows she can be her true self around MC and be accepted, to the point she told him something she probably hasn't told another soul, she wants to explore 100% monogamy with him