Dear ...
I’m writing this letter to offer encouragement to you to move to __(location)__. I think it would be wonderful for you and your family to come here both as an opportunity for a new start and to enable you to more easily visit your __(son/daughter)__. I know __(Child’s Name)__ would love that.
Times have certainly changed since we were last together, haven’t they? We’ve both moved on with our lives, each marrying someone else and starting new families. Yes, things are different from those days when we shared our lives and our love together. I cherished our time together and I have to say, it did take me a long time to get over you. But, I want you to know, that despite the pain of __(you walking out on us/having to let you go/etc.)__, I hold no malice towards you. To be honest, even after all this time has gone by, a piece of my heart still belongs to you. You will always be my first and one "true" love, __(Name)__.
Now, however, our relationship is different. We come together once again, this time as friends because now it’s about our __(son/daughter)__ and having you in __(his/her)__ life. I think you would be surprised to see how much __(Child’s Name)__ is __(his/her)__ __(father’s/mother’s)__ __(son/daughter)__. Not only does __(his/her)__ mannerism mimic yours, I often see your reflection when I look into __(his/her)__ eyes. But it should be about more than just resemblance, __(Name)__. It’s time for you to have a relationship with your __(son/daughter)__. To be an influence in __(his/her)__ life, not just to bear a resemblance.
I genuinely hope that it works out for you and your family to move to __(location)__. That would be a blessing in so many ways and I will remain hopeful that it comes to pass. Take good care.
Sincerely yours,