Happy Ending G

Mary is an old woman who falls in love with John, and John who is a mid-teenager.
One day, while John was standing in the street after school, he saw an old woman was crying sitting on a bench near the lake. John thought she wanted to (kill herself / end her life - either, but not both) Therefore, he yelled at her. He said "Don’t be silly by ending your life, the world is still beautiful. Every terrible things must can be resolved, so keep calm your mood down and come over here."
Mary walked close to him. She felt strange, she did not want to commit suicide. She told John she was crying because her older cat died, and went to the lakeside to take her out of herself. John felt embarrassed. He said "Sorry," and then silence. Mary told him it’s OK, don't worry about it.
John smiled, he was thinking Mary is an entertaining person. He wanted to make friends with her, so he decide to invite Mary on a date, and Mary accepted John's request.
After a few dates, John gradually fell in love with Mary. He sensed that she had a beautiful heart and she is kind. Mary was thinking John is an adorable guy, so they stayed together.
Eventually, they died. This is the end of the story.

This is a nice story. The following are the corrections.

Green - capitalization. The word okay is lower case, but the abbreviated OK is upper case.

Blue - incorrect tense or missing parts of speech.

Pink - awkward word choice.

Orange - punctuation, including sentences that should be separated.