Most Helpful Guy
I thought you were the bitch at beginning, but seems like the real jerk in this story is the so called "BFF"... What a cunning and deceiving rat...
I had the exact same thing happening to a friend about 10 years ago actually.
Let's call him L, and his (fake) best friend will be called K.
my friend L got dumped by his girlfriend. A few days after, we realized that it was mainly because K talked to L's girlfriend (saying she should dump him and sh*t).
So litterally K revealed to be a f***in traitor, and on the top of that it appears he was attracted by L's girlfriend...
Generally speaking, it is highly insultive and disgusting to dare creating a connection with the best friend of a guy you just dumped. He's is your ex bf's ally, NOT yours.
HOWEVER, a REAL best friend, would never accept to be friends with you after you dumped his buddy in the first place.
So that leads me to the conclusion, this "bff" is one hell of a traitor because everything he did was to help you, and never to help his friend (your ex).