Dreamed that his girlfriend was dead.

That's right. Whether you accept it or not, death represents a new life in the subconscious of dreams, and water is the most direct expression of the subconscious. In other words, you have completely let go of your relationship in your heart. Although on the surface you haven't walked out of the shadow of your feelings, in your heart, you have accepted the reality of this breakup. I also believe that your inner pain has been struggling for a long time before this reality happens. This breakup is one of them.