I've had an Nfriend try that...I dunno if she succeeded we broke up, what he said it doesn't sound like cause of her, but she was dating someone else by then. Her only reason for going after him was because she was angry that a guy was smitten with someone who wasn't her. It had nothing to do with him or me but her. However, after this, she started lying about me to my friends so suddenly I was losing friends and suspicious...a loyal friend confirmed my suspicions.

She had a 2 year old daughter at the time, and I feel severely sorry for the kid because unless Mama cools off with age, she is going to lose her shit when her daughter's beaus find her special. And she is going to do anything to make them fall for her. (She was in her 30s, and yet she did what she did to me--20s--to a 13 year old girl, making underage boys luff her.)

My Nfriend tried to sabotage 3 infatuations, one where we were both in love, my rebound guy who loved me but I didn't return his ardor though I tried, and finally a guy who was a great friend who I had a major crush on but I was still madly in love with Guy A (he's not just a guy to me). She didn't really succeed unless Guy A fell for her, but she sure as heck tried.

Far as your stories go, they really are anger-inducing. Ns should butt out of other people's relationships. Romance ends a lot without their interference. But it's fun for them to screw things up for people who don't see where their hands are.