ME TOO. Yes, seems like when you hit the 750 mark. I just gave it a go with Jean and she said yes. Then the next day she drags me for private talk she says she's been a virgin too long.Update on my case... At around 700+ love/trust, I finally got Rogue to accept poly, but I noticed it happened when I reached the summer chapter, dunno if its a requirement but it's what worked for me
It is correct that it is important to complete the optional quests before progressing, unlike the "Dating X" quests these don't carry over to next season/stage, and they do gain a lot of points. I did spam swim a few times and yes had a fair amount of flirting etc.
I just realized I shouldve been more invested in Rogue given the updated graphics... we'll see if it'll be worth replaying from the top at some in the updates, but I doubt my fingers will ever miss Jean as the axis relationship.