To get the orgy, you need to do the following:
Drive to Aria's place. Accept her kiss on your lips. Stay and watch. Get a taste. Offer Henry a taste. Ask Mark to forget it. Mock Henry at the pool. You'll join them, but keep your bra on, and go to sleep. Angelica will reject Aria the next morning. At breakfast, choose "Henry needs you!". Take Mark's money the following day, and make Henry feel like shit during the workout ("it's the effect of having a real man in the house"). Accept Mark's offer about the hormone drugs, and tease him during the workout. Keep humiliating Henry during the dinner, and wear something revealing the next day.
When Mark confronts you about it, choose "it's all my disorder Mark". Later that night, invite Henry to join you and Aria at the club, which will lead to a disappointing threesome. After the truth comes out, you'll get to choose to go out with Aria, and that leads to the orgy with Julia, Angelica's sister. However, it's not really an orgy, because none of them change partners, and there's no lesbian action between them. Oh well, hopefully next time.
So there are at least 5 distinct play-throughs that I encountered: the total whore path (accepting Mark and Aria's advances, cheating on Henry early on), Aria's love and domination paths (by rejecting Mark as a friend, and accepting Aria), the cucking wife path (by teasing Mark, but ultimately rejecting him, having the threesome with Henry and Aria, and staying with Henry during poker nights - which leads to a strip tease for Henry's friends), the fed up wife path (explained above, which ends with the "orgy" scene), and the good wife path (by rejecting everyone's advances, and remaining faithful to Henry).
I don't know if there are any more paths, but there are definitely renders I haven't seen yet.
Anyways, I hope that helps.
Cheers.
