I am not speaking for everyone. But
The Rule is not about the guy. Whenever a relationship ends there are some left over emotions no matter who ended the relationship. It is usually a little uncomfortable to see the ex with someone else. Even if it was you that dumped them.
The Rule is there to protect friendships, you can tell yourself to quit feeling that way, and that it is not rational, but it probably won't do any good. And a good friend is aware of this, and will not want these issues to divide you. It is easy to get over the ex moving on when we are talking about stangers, we have no daily contact, it is not something we have to think about. When it is your friend, your friend wants to talk about her new relationship, or gossip. Not really a comfortable situation.
I am still catching heck about a rule violation with one of my sisters. And I don't think I broke the rule. But there was a technicality (we met the same guy at different locations and times, and acted like he liked both of us. I ended up hooking up with him, so I received the violation). And this was about 9 years ago. They don't forget.
