There is no single construction here. What is reliable is the 는데 ending itself, which softens a sentence by leaving it slightly open: it is a once-in-a-lifetime thing, so of course I am going. Worth learning from these lines is the stock softener meaning sorry, but, which opens a request such as could you please leave. Three of the printed lines do not contain the verb 가다 at all, only words that begin with the same syllable.
The examples below did not fully pin this one down — read them before relying on the entry above.