We 've nearly been stranger for quite a long time...
Maybe it is too late to say anything about that old rela. I just want to express what i 've really wanted to let you know.
You were in my life in the best time of my life. The way you cared about me is something that nowhere to be found. You even made me think that no matter what I had done, who I would be, you still loved me the same. 
I think that at that time I did feel your love but I didnt know how to appreciate it. Many years later, I gradually realized how bad i was and I didnt deserve you at all.
Time flies, everything changes, we 're all fine and have new life not related to each other. I've always thought about one day, i can stand in front of you to say "Thank you" with all my respect but it seems impossible bcs i dont want to bother you anymore. I know that this "thank you" means  too much to me but nothing to you now. 
If I am asked whether I feel regretful or not? I am not sure with my answer!
Btw, I am OK with my life now. Its too good to ask for more...
But one reminder I will keep for myself is "IOU"!