One half will prove to have a stronger will than the other. The less dominant half will then weaken over time, and it will eventually 8ecome clear to 8oth that one will not survive. The dominant personality will then completely consume the other, integr8ting it in such a way that only one is left. The cheeks will 8ecome solidly colored, and the cheru8 will grow to maturity as a single 8eing, endowed with the alignment of the dominant half, and with all his or her personal qualities at the forefront of the union.
In the case of our heroine, she was the good half, and the day of her predomin8tion was in a sense the day her 8rother died. And though it was to her 8enefit and personal growth, 8ecause of this loss she would always live with a sense that something was missing. Every sexually mature cheru8 lives with this feeling. It drives them to seek out another cheru8 similar to the half they lost, the part of their 8eing which they grew up in perpetual conflict with. The desire to travel the universe in hopes of reigniting that conflict is very important to their species. It's the force which compels them to procre8.