Help me find this oneshot

There is a oneshot that I read in fb loong time ago.
The title is something like 'love letter' but idk--

The story begins with a child that was born to a young mom. She didn't really care for the child, despite the child being so bright and happy all the time. When the child was like 5, she decided the leave the child in her locked apartment and went to live in another town. The child was found by police weeks later, dead.

Then the next scene takes place in heaven. The soul of the child before is being asked by an angel. The angel asked him what he wanted to be reincarnated as. The soul then answered that he wanted to be born as a cat. When he later was born as a cat, he found his mother again, and stayed by her side.

The reincarnation keeps repeating until for the last time the soul asked to be a drop of rain. And that drop of rain whispered to the mother that he loved her, when she was going to jump into a train.