Aubrey is, strangely enough, more desirous of commitment than the other girls but also more afraid of it. This is because of how her family treated her all her life, with her never being good enough for her parents and her sister taking everything away from her. Even her dreams. Her self-image has been savaged. This complex made her keep all men at arms length because she was afraid to lose them like she loses everything. That's why she is crushed when you have sex with her sister, even though she was the one who resisted commitment. She thought that she could have one thing that her sister couldn't take away and she was wrong. This is also why you have to step so carefully when you are on her path. She has convinced herself before the relationship even starts that she has already lost.
She is the easiest girl to sleep with and the hardest girl to get to be yours. She kinda reminds me of Mary Jane from the Spider-man comics. Not the shitty movie version, mind you. The devil-may-care party girl with a tender heart underneath. An unlikely one true pairing, but perhaps the sweeter for it. She needs those little moments, not big gestures. For you to leave Emily downstairs so you can talk to her upstairs. For you to throw a pebble at her window like Romeo. A dance in the park. For you to leave Nora at the warehouse so you can care for her leg. For you to give her flowers and the photoshoot and chocolates at the beach. An invite to a concert. A three-way kiss with a dairy cow. For you to sneak away with her to a secluded cove and teach her how to swim. She knows that you have options that are smarter than her, prettier than her, more faithful than her, and even more fun than her. If you do choose her it might be the biggest surprise of her life.
I think that Riley is finding out the same thing that you have. Getting in Aubrey's pants is far easier than winning her heart. If the three-way relationship that she wants is ever going to work, Riley is going to have to work as hard as MC has to convince Aubrey that it is something real. That it is more than just another thing for her to lose.
