Juliet is on her balcony and bids Romeo goodnight with the words, "Parting is such sweet sorrow." This phrase is such an oxymoron that combines contradictory ideas of pleasure and pain.
I would imagine that Juliet's heart longs for the following day to see her
Romeo, and that is why she can use the words, "sweet sorrow."
For myself there is no tomorrow, and yes this does bring my heart sadness. However, the sweetness of the farewell is that I have been strong enough this time to do the "parting," and to not hang on by that thread of false hope that things will change.
I believe by writing these words down they will be a declaration that I have done the right and loving thing for myself.