too long and homophobic (SPOILER)

I did not really read the ending that way at all. I think Mew came out okay - as symbolized by the toy, he (with Tong's help) was completed. He had moved past his losses (of his parents and grandmother and Tong himself). Tong had shown him the magic of friendship and the miracle of love. Mew had his friends in the band (and possibly a new romantic interest with the one). So he ended by thanking Tong for showing him the possibility of love.

Tong on the other hand faced (in my opinion and based on experience) a terrible struggle to be himself, escape his mother's emotional stranglehold and find a love that might match what he had with Mew.

(I agree that some judicious editing might have helped, but the Tong-Mew dynamic made the film run quickly for me. I was enchanted right from the prologue - especially the treasure hunt sequence where Mew comes to understand Tong's affection for him.)

"Nothing personal. Your name just happened to come up."

so was puzzled as to why Tong rejected Mew in the end.

But Tong didn't reject Mew. He just can't be his boyfriend. By saying he loves him, he's acknowledged Mew's love for him and his own for Mew. They will never be alone again, in that sense.

Going even further Mew, the one who is more accepting of his sexuality is shown alone and weeping in the end while Tong is back at home with his family receiving love and acceptance.

Wow, your interpretation is so interesting. In my view, Mew's not alone. With the wooden doll completed, himself is emotionally completed and is able to move on. That's why he smiled while he cried.

Did you not remember their first long conversation about loneliness? Tong feels alienated from his family because of Tang's absence, his mother's controlling nature, and his father's grief and alcoholism. He had problems with his girlfriend Donut and getting close to people because he was afraid of experiencing what his parents are experiencing. This is the same problem Mew has.

Mew feels alienated because his rep at school as a 'sissy boy', his grandmother was gone and his parents absent. He's afraid of loving then losing someone; like his grandmother.

They are drawn to each other, partly because they are childhood friends (remember Mew's repeated statement to Tong's mother "We are just friends") and because of that, they feel complete together.

Mew's best friend, whom he had been alienated from after that kiss-of-life joke, reminds Mew that he isn't alone and that there are people who care for him. Then there is Tong who accepts Mew and himself as they are.

I thought it was an optimistic ending. Both boys were once lost and now they were found, they could move on with their lives and not to feel so lonely any more.

It's fair to acknowledge the film's attempt to explain that it's a fluid thing. It doesn't automatically snap to either black and white. Like either you know or you don't. Not everybody is that "lucky". I truly believe everyone had experienced this at least once in their life, whether they realized it or not and however long the experience was.

For now, The Love of Siam did an incredible job, opening a door to make way for future teen gay films with, likely, happy endings. This film has made the first major step to a better world, so now it's up to Thai filmmakers to take further steps ahead.