My ex started dating one of my friends, no one told me about it until I saw them holding hands walking down the street some 4 months after the breakup. Although if the break up was nasty or your friend still had feeling a for said ex, as a friend, it's pretty low to go behind your friends back knowing there are still feelings. A good friend used to say to me, "You're on your own road. And now she's dating him. I love this, I agree: They will support you more than you could have possibly imagined.
Wish them well and find a new friend.
My Best Friend Is Dating My EX Now, And This Is How It Feels
I agree the "girl code" rule here should expire after a few years, because I don't give a crap about my exes from that long ago, but this was my most recent ex. Whether this is a deal breaker and you want to cut them out is entirely your call. I hope you understand that we don't want to hurt you. But from her responses, it appears that wasn't it. Yes it was wrong of them to hide it from you but frankly he is not your property and can date whoever he wants. I'm sorry that you are going through this. People in this subreddit are so immature.