This farewell letter can be used to end a relationship, friendship, or business partnership.
Dear {Recipient},
I'm sorry to have to write to say goodbye, instead of seeing you in person or at least picking up the phone, but I think it's just easier for both of us this way.
I hate saying goodbye. But I'm trying to focus on all the fun times we've had over the last {length of friendship, relationship, etc.} , and those memories are giving me some comfort. I like being able to look back on something and smile, and that's what I think I'll always be able to do with us.
This isn't a forever goodbye. While I don't know exactly when we'll see each other again, I do know that it will happen. In the meantime, let's both try to focus on the positives in this situation. You {something good happening to the other person} and I {something good happening to you}.
Let's make a promise to keep in touch and keep one another informed on the progress of our lives. And then when we see each other again, it will be like we were never apart.
Talk to you soon,
{Sender}