Ladies, why would you date a guy you talk negatively about to another guy?

So odd situation, a friend of mine is dating a guy that she always talks down about. Such as I'll never get into a relationship with him because he ignored me when he dated someone else. She has mentioned that he has fallen in love with her but she isn't ready to be in a relationship with anyone. Since this started I noticed myself starting to catch feelings even though I'm not interested in dating because of a recent bad breakup.
So my question is do you date guys even though you have no intention of taking any further than casual dates knowing the guy is catching feelings for you?
Ladies, why would you date a guy you talk negatively about to another guy?
Ladies, why would you date a guy you talk negatively about to another guy?
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