What is a perfect complimentary astrological sign for Saggittarius?

I am a Sag., my wife is a Cancer. according to everything i have read, we are the exact opposite signs of compatibility for each other. yet, we have been married for 44 years. what happened? are the astrological signs incorrect? how are we still happy together after all these years? what is the correct astrological sign for a Sag.?