I cannot understand X's appeal nor her success with men. But she sounds like she's fiercely competitive with other women. She deliberately marked her lover's home with her "scent" (bra, tampons) to send his wife a message. It galls me that people like her trample on others and get away with it. I hope this dope she's seeing turns out to be bankrupt and that they make each other miserable.
A few years ago I had a friend -- a good friend, I thought -- who was divorced like me. She always spoke as if she was a feminist. Ha! I told her all about a guy I was dating from match.com whom I was crazy about. Every time she and I got together, we confided about our sex and social lives, and I updated her about my goings-on with this guy. She listened and voiced empathy. Oddly, I thought, she invited me to a concert and refused to let me pay her for my ticket, and she had me over to dinner. Shortly after that, the guy broke up with me. I don't want to bore you with the details, but suffice it to say that I learned she had been seeing him behind my back for weeks, during the time that I was confiding to her about him. When I confronted her with my suspicions, she self-righteously confessed and went on the attack, screaming and yelling like a madwoman. I hope she rots in hell along with X.
Looking back, I now see that it's her pattern to appropriate other women's men. I recall her telling me about a guy she'd had a year-long relationship with. Eventually she broke it off, and he was heartbroken. Six months later he had a new girlfriend, and she learned that the two of them were planning to spend a few weeks on Nantucket that summer, an island that she frequented in the summer as well. She was furious and told him he couldn't step foot on "her" island with his girlfriend. Then, to make sure that wouldn't happen, she seduced him, claiming she missed him and wanted to try again. Suddenly he was irresistible! She slept with him a few times -- enough to destroy his new relationship -- and dumped him.