I am not sure I understand the thing even now. If two persons once held hands, kissed, and said sincerely that "I love you", after they break up, how could they look at each other as strangers or worse?
Is it easy to forget a person in our memory? Why are people clear and smart enough to move on and never look back? Isn't it cruel to another person?

They could act like strangers but deep down, they won't forget easily. They just want to protect themselves from pain, or they might not want to hurt the other person. So its very common to see this phenomenon.

Its called picking up the pieces of your own life, and moving on. Sometimes things don't work out for us, no matter how bad we want them to, so we move on with our life, and look to the future, and remember the past. Anything else would be what we call "stuck" (on stupid)!! Sometimes when we are caught in the middle of these emotional storms, we feel so bad, we can't see the sun, or blue sky, or the happiness thats waiting for us. We never forget those we leave behind though.

Its strange really because I've just had a baby a few weeks ago and I'm not with her dad any more.we split up when I was just 3 months pregnant. We used to tell each other that we loved one another and we spoke about weddings etc. we still see each other as friends and obviously he sees his daughter but apart from that, evrything that we had together before just seems like so long ago. And I never look back on it either. I'm single, I've moved on. My situation really is just like I have had a baby with one of my friends!

I think that as mutual as a breakup is there is always one person that wants it more than the other! Because of this it is often very hard to continue to be friends and see/speak to that person because of all the good memories it brings back. Sometimes it's just easier to kill the relationship and just keep the memories deep down inside.

Generally in time as each person moves on and builds there life up it becomes easier and easier to become friends again... however in my experience the chances for this to happen can already of been ruined after the early stages of this cycle!