I've learned to let go of a lot of things and believe me, it wasn't easy. There are steps to doing this...well, at least for me there was. First I had to know what was really bothering me, what my source was, reasoning it, accepting it and then come to my own conclusions of why and move on. Although I think that forming your own opinions on something without having a true conversation about a problem can get tricky.
I think a discussion or just bringing things out in the open would be a better healing practice than just brushing things under the rug and "pretend" to move forward. I think you're doing a disservice to yourself and your growth if you don't fully talk about things that have bothered and haunted you for so many years. But, I know that sometimes this isn't possible and some people just don't like to talk about things so what happens to you then? This is where the "forming your own opinion" comes in. What else can you do right? Like I said, it's tricky...not so black and white. Everyone has their own way of coping, of accepting, so who are you to say if that person has moved on or not if it's not affecting your life, right? Whether you do it in a healthy way or not is totally on you. You are the keeper to your conscious and whether or not someone else has an opinion on that is just that...their opinion...some we treasure, some we care not for.
Assumptions are the worst thing you can do to someone, especially when you're wrong. I was talking to a friend who put it in the greatest way. She said, sometimes, people take snipits of your life and freeze them, they end up assuming who you are and who you'll be. Sometimes I'll have conversations with people and they'll make a comment about me in some way and I think... 'hmmm, is that how they've thought of me all this time? Shows how much they know me'. Do I go out of my way to prove anyone wrong? No, don't care too because how they form they're opinion of me has no effect on my life. I just think it's interesting when someone blurts something out and is insensitive about their assumptions, without truly knowing the facts.
I guess what I want to say is that, it's ok to talk about the past, make peace with it and know that deep down in your heart, you've already made peace with it. Now if you're always bringing it up, you're always harping on things then you haven't found moved on yet...and guess what...that's ok too because at some point you will. We are all different, we all heal differently, we all have different ways of dealing with things and that's OK. If you love someone, you will be understanding, you will be forgiving, YOU will not judge and be insensitive. Be supportive of someone who is not at peace because their time will come and don't assume that they haven't made their peace either. Assumption is the killer of relationships or your judgements and so you should kill it, right now.
And yes, some people never move on, never heal... but what can we do right? But take care of our own healing and our own process, our own growth. Evolution is an amazing thing! It makes us more sympathetic, more aware of people around us. You never stop learning... and when you do... you're just dead.