Hmmm, the MV didn't tell lots of things that really happened.
I'll try my best on translating the story.
Fah and Tan, and they are close friend for over 10 years.
Tan always take good care of Fah, and Tan never denied when people are calling them a couple.
Fah secretly love Tan, but she never told him because she is afraid of losing him as a friend.
Tan also never told Fah how he feels.
After they graduated, they go and live their own lives and havn't met for years.
One day they met each other by chance, they had dinner and they slept together.
(Which is not normal thing when this happens with a friend.)
After that, Tan called Fah and tell her he is sorry.
That apology makes her feel like Tan didn't mean to do that.
So, she told him not to apologize or talk about this again.
After that, they are not talking like usual.
After months pass, Fah realised she has a baby, but she still hadn't told Tan.
She heard from her other friend that Tan is getting married.
So, she decided not to tell him, because she knows Tan is a good person and he would be with her for responsible of their child. She doesn't want to make his life change, also she doesn't want to make him being with her because of he has to responsible, she wants him to be with her only if he loves her too.
(In Thai, it's not normal for a father to pay for a child but not being with them. If a man are a father, he should/must responsible by marrying with the mother.)
When they met after she has a child, he was shocked.
He asked her who is this kid, she answered it's her daughter.
He was shocked and stay silent for a while and then ask her if this is his child or not.
But, Fah denied. (I don't know why she denied at this point)
Than after they finished lunch, Tan told Fah he is going to marry. (No wedding card like the MV)
So, that makes Fah thinks she shouldn't be invloved in Tan's life.
(If she tells him, he will come to live with her for sure, but she doesn't want that if he doesn't really love her.)
And, one day she called to radio program that people can talk about their sad story.
By chance, one of her friend listen to the radio and think that it's Fah.
Because she knows Fah, and Tan. She knows Fah was pregnant but Fah told no one that who is the father, not even her family. And Fah never has any boy friend, she has only one close friend, Tan. So that friend called Tan and told him what she heard from the radio.
So, Tan was sure that this is his daughter. So, he came to Fah.
And he told her that actually he loves her since they were in University.
But he never told her because he didn't want to lose her as a friend too.
He told her he decided to tell her the day he is ready for her.
Actually, after the night. He wanted to tell her how he feels.
But he had a girl friend at that time so he had to clear things before he could tell Fah.
Sadly that Fah weren't replying his calls because she though he is getting married.
And they day they've met (with the child).
Tan thought Fah left him. So, he told Fah that he is getting married.
Also, Tan told Fah that he will get divorced and come to live with her.
Fah denied because he is married and he shouldn't left the other girl.
Tan asked him to be around and pay for the kid,
Fah also denied because they have feelings for each other,
it's kind of impossible for them to continue meeting as friends.
And Fah doesn't want to be a secret wife or anything like that.
If Tan never loves her, she might say okay for him to be with the kid.
(So, the child will be a single mum's child or either be a secret wife's child.
Then I'm sure the first one is much better than the second one)
Fah said she will tell her kids that she was born because of the love of father and mother.
But they have their reasons that they couldn't be together.
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I think this can make the story easier to understand.