“I recently found out one of my wife’s good friends spread a rumor about me that is totally untrue. I was completely alarmed when another friend mentioned she heard this woman take a shot at my character—and that it was not the first time. It’s possible she has some unresolved feelings for my now-wife, who she dated on and off for three years before we got together. But, how do I put an end to this?”
Staying friends with an ex is tricky, especially if the breakup wasn’t exactly mutual or one party still has unresolved feelings for the other. Your wife is probably oblivious (or purposefully ignoring) the dicey dynamics here. It's hard and painful to say goodbye forever to someone who was a big part of your life, so your instinct that this has something to do with unrequited love probably isn't too far off.
You have two options. Bear in mind, one is probably better than the other.
Option #1: Approach the issue yourself.