Hello, I'm looking for this chinese movie/drama (I saw a clip of it and can't find its title) about: 

- a guy who fell for a transfer student at first sight (he was in elementary at the time), her name is Xiao Mi (iirc) and proposes for marriage which she promptly refused saying she wants to marry Justin Bieber. 

- He kept wooing her by asking if he helps her with stuff, will she marry him and she keeps refusing and this goes on til they're teenagers(?). 

- There's a scene where the guy proposes to her by saying "if you're still single by the age of 60, will you marry me?" to which she replied "No! how could I still be single by then!" And he retorted "because you haven't married me yet!"

- i think this has bittersweet or tragic ending, the guy might have disappeared or died(?) as he turns into dust in one scene.

This might be super vague and super detailed at the same time but the clip doesn't give out names/sauces and I'm going crazy trying to find it.

Not sure about Justin Bieber part but I think it's Till We Meet Again, a Taiwanese movie with Ko Chen-Tung

Thankyouu, you saved me from a sleepless night! It should be the one you mentioned.