That song would definitely be 好久不見.
好久不見 means, literally, “long time no see”, and in English has a flippant, jocular feel to it. In this song, however, it’s more sincere, wistful, a regretful “it’s been a while”.
我來到 你的城市 走過你來時的路
想像著 沒我的日子 你是怎樣的孤獨
拿著你 給的照片 熟悉的那一條街
我會帶著笑臉 揮手寒喧 和你 坐著聊聊天
不再去說從前 只是寒喧 對你說一句
I’m here, on this street, walking where you walked.
Thinking about how lonely you must have been.
Looking at the photo you gave me, of that familiar street.
Without you in it, the picture is not complete – we can’t go back to the way it was.
If you showed up at that cafe on the corner, there
I’d smile, wave, and call out to you.
We’d sit together, and talk of inconsequential things.
How wonderful it would be to see you again, to catch up with each other.
We’d put the past in the past, if only I could just talk to you,
If only I could just say…”it’s been such a long time”.