Would you confess to a girl you like before you went to separate

Depends on what you mean by confess.

If you mean sperg out and confess my undying love then hell no.

If you mean to tell her that you like her as more than a friend, etc, then sure. I did that once with a girl when I knew i'd be moving away. Of course, she was already taken so I didn't expect much, but I figured i'd do it and see how it goes.

Tl;dr it's all in how you do it. Don't come off as a desperate or obsessive weirdo

as said in all animes:

to do something stupid is better than doing nothing at all