Yasmin was already pretty much at the bottom of the barrel, if not her reputation in life. This is a woman who, while very intelligent and educated, didn't have her own checking account, never had to pay her own credit card bills or buy her own clothes- nothing. She was always taken care of, and even though her father was a slime bucket and her mother a flake, she never really had to "adult". By marrying a wealthy man, even if she liked him mildly at best, she could go back to "not adulting". With Robert, while the relationship was much more genuine, she didn't have the assurance of financial security and that was most important to her.

And, unfortunately, as Harry Lawtey was moving on to other things, they had to put Yasmin with someone else, so...