Time will heal all wounds, is what they say, but what my own experience is as well. Accept the past (since the past can never be changed unless we get our hands on a time machine of some sort), and move on. That said, reading the way you write about your ex, I do wonder if you shall not send that last letter. I mean, sure, perhaps looked happy and all with the new 'love' in life, that doesnt mean anything in terms of both of you.