Carolyn Hax: He likes two girls, and plays one against the other
Adapted from a recent online discussion:
I'm seeing a guy but we are not yet exclusive. He is concurrently seeing another woman who is pressing him for a commitment. I am starting to get the feeling he is using me to leverage her, implying that if she pushes too hard, he will just pick me. To what extent is it my responsibility to get my guy to act more respectfully toward this other woman (whom I've never met and don't particularly like, based on his descriptions)?
Having + eating cake
If I've read this correctly, he's dogging one steady companion to another. Your only responsibility here is to avoid abetting people who are either two-faced, or too cowardly to break up with people they don't actually like, or both.
If I've misread it, and he's speaking fondly of her but you just don't like the person he describes, then that's a different answer: His talking so much about her on dates with you is unfair to both women.
Either he likes both of you and is seeing where things take him, in which case he's too clueless or thoughtless to keep the details to himself; or he's deliberately leveraging both of you.
In other words, if this whole other-chick subplot is anything more than a conversational ort relative to the cake of your time together (see, I can torture a dessert metaphor, too), then that's a bad sign.