After Mimi left, Arianna was disturbed in the spirit. It was as if her best friend had stirred all the unnecessary feelings she had buried deep inside of her.
Could she have a sexual relationship with Marcel? She means sex and real feelings were too different things, right? She could sleep with someone and not have feelings for that person.
Moreover, Elijah wouldn't even know unless she told him or Marcel whines his big mouth. Also, what's the probability Elijah was still faithful to her since they separated?
No, no, she can't think this way. Mimi could do this but she can't. Unlike her, Mimi was the wilder one, as unrestrained as the wind. Two people can never be the same, so she had to adhere to the principles she had grown with all this while.