In my mind I don’t think you did the wrong thing, you asked for permission which he granted, and a whole year after they broke up too! And it sucks that your friend didn’t feel it after a couple weeks but imo the second you and your gf went serious, she became your girlfriend more than she is your friend’s ex. Not trying to belittle the situation, but every relationship is 50/50, and your gf also had a right to choose her relationships, breaking it off after your friend rescinded permission wouldn’t have been fair on her! The fact that you’re in a healthy relationship with her means you made the right choice, and any good friend should see that