The split you are looking for is when you can choose to "Spend the day with Andrea" or "Go find out what Natalie wants." The second option will open up the dom side of that path.
Assuming you don't mind spoilers, with the dom path instead of making Milly passive it makes her aggressive. They go back to Andrea's house and she screws her a couple times. Milly tells Andrea at the end that she owns her now (paraphrasing). I definitely prefer this one over the sub, which was still good but made me a little uncomfortable with how it went down.