I believe “Love of Siam” didn’t have a bad or sad ending, it’s OE. It’s just about the time. As can be seen from the movie, we can see that at the first time, Tong’s mother didn’t allow Tong to remain the relationship with Mew. However, when Christmas came, his mother asked him that what he would choose and Tong chose the male doll, which means he loves a man. His mother replied to him that he should choose what made him feel happy. Because of that answer, I believe that the fence stopping his relationship with Mew was broken. Nevertheless, why he said to Mew that he couldn’t be Mew's boyfriend but it didn’t mean he didn’t love Mew. In my opinion, he had to choose his family first. His father has a serious disease, his mom is the only economic pillar in the family. His responsibility at the moment is to take care of his parents. He can’t put all of his mind into love business now. Especially, even though Tong has permission from his mom, but she still needs time to get used to it. Let’s imagine if he and Mew were lovers, then his mom could feel uncomfortable, combining his father’s problem, she could be very stressful. Tong just don’t want his mother to suffer the hardness alone.
In conclusion, I have an extremely strong belief that in the future, they will be together again. At that time, Tong’s family already get through their tough time. Mew and his band become successful.
They were just high school students at that time (2007), they’re learning to grow up. Now is 2020, which means 13 years later, perhaps, they’re together