To activate the event chain to achieve this harem you have to meet the following conditions:
Invite Sasha to a date in the nightclub. This event will only trigger if Audrey is also at the club at the same time. You can check Audrey's time schedule (currently, Sunday 12 AM to 5 AM) to see if when she is in the club.
In the nightclub Sasha hears a song she wants to dance to, so she drags Mike onto the dance floor. Mike can soon feel someone pressing their body against his own which turns out to be Audrey instead of Sasha. Sasha gets mad, turns around and starts to storm off. Audrey realizes what just happened and steps aside to allow Mike to follow Sasha. He reaches Sasha and has to decide if he either admits that he cheated on Sasha or not.
Apologize to Sasha
After Sasha found out about Mike cheating on her with Audrey, Mike need to find someone to talk. Therefore Mike has to talk to Samantha to progress (you have to at least show Samantha the evidence that Ryan cheated on her!) OR (you have to be on Samantha's Revenge Path). In the Dialog with Samantha she tells Mike that the only one who can resolve this problem is Mike himself.
After Mike talked to Sasha the problem is resolved and Sasha won't tell Mike to piss off anymore.
After you finished the initial events there are a few more conditions required to progress:
Audrey has a proposal
To progress further in the event Mike has to go to to work and either work or work hard while Audrey is also present. She will put Mike in an situation where he can't escape from her and asks him why he is avoiding her lately. She proposes to Mike that he, Sasha and Audrey should have a threesome.
If Mike doesn't accept the proposal then the jealousy harem will end right there.
Talk to Sasha
After Mike has accepted the threesome idea from Audrey he has to talk to Sasha (you should see an extra icon when talking to her). They will talk about the incident at the nightclub again before Mike asks Sasha if she would be ok with having a threesome. Sasha accepts after thinking about and Mike tells Sasha that because Audrey is the new one in this situation, she will be in an inferior position.
Talk to Audrey
After Mike has Sasha's blessing for the threesome, he tells Audrey the good news (talk to her at work, there should be an extra icon). Audrey somehow has predicted, that Sasha would accept this proposal and the they agree to meet on the next Saturday at Mike's house at 14:00.
(you need to manually trigger the event by clicking on the date icon) Mike and Sasha sit in the living room waiting for Audrey to show up.