wow, You asked a good question. I believe that nature returns the way we serve. So its better to have a grief than to make someone sad.
This. It's really not about which one of the two is better or worse. It's about what needs to happen in order for the two people involved to improve their lives as individuals. So, sometimes you need to break their hearts especially because you still love them and respect them as people. In which case it isn't done to hurt them, but to protect them from further emotional grief.
Glad to see my post here is still relevant to the discussion. I still stand by that statement by the way.
If you're a good, kind, caring person, even breaking the other person's heart will affect you. At the end of the day though, I like to think of things as simply sharing time with people, some more, some less - you can't expect forever with everyone you meet, and that's ok.