Dear Prudence,
I’ve been casually dating a man for the past three months, and we recently attended an event with several of my former colleagues. The man I’m seeing has some intersecting social circles with my colleagues. While at this event, he informed me that a woman I know gave her number to him. She’s in a committed, live-in relationship with another former colleague. Since my relationship is new, we have not yet been vocal to this broader group about exploring and enjoying each other’s company, so I don’t really have any leverage on my end. On her end, however, she is in a committed relationship. Should I broach the topic with her partner and inquire as to whether they have an open relationship? Am I being old-fashioned to feel that she should not be sharing her number to other men while she is committed? It’s worth noting that this woman has a track record of infidelity and misbehavior.
—Murkily Suspicious