Some quotations about siblings that you might find helpful on those really difficult :( days -

Our brothers and sisters are there with us from the dawn of our personal stories to the inevitable dusk. ~Susan Scarf Merrell

Brothers and sisters are as close as hands and feet. ~Vietnamese Proverb

I, who have no sisters or brothers, look with some degree of innocent envy on those who may be said to be born to friends. ~James Boswell

I don't believe an accident of birth makes people sisters or brothers. It makes them siblings, gives them mutuality of parentage. Sisterhood and brotherhood is a condition people have to work at. ~Maya Angelou

A sibling may be the keeper of one's identity, the only person with the keys to one's unfettered, more fundamental self. ~Marian Sandmaier

Our siblings push buttons that cast us in roles we felt sure we had let go of long ago - the baby, the peacekeeper, the caretaker, the avoider.... It doesn't seem to matter how much time has elapsed or how far we've traveled. ~Jane Mersky Leder

Our siblings. They resemble us just enough to make all their differences confusing, and no matter what we choose to make of this, we are cast in relation to them our whole lives long. ~Susan Scarf Merrell

Sibling relationships... outlast marriages, survive the death of parents, resurface after quarrels that would sink any friendship. They flourish in a thousand incarnations of closeness and distance, warmth, loyalty and distrust. ~Erica E. Goode

Siblings are the people we practice on, the people who teach us about fairness and cooperation and kindness and caring - quite often the hard way. ~Pamela Dugdale

To the outside world we all grow old. But not to brothers and sisters. We know each other as we always were. We know each other's hearts. We share private family jokes. We remember family feuds and secrets, family griefs and joys. We live outside the touch of time. ~Clara Ortega