For there to be completely happyness in Marriage.. The man and woman must be one.
The bible says in Genesis 2:24 "Therefore shall a man leave his father and his mother, and shall cleave unto his wife: and they shall be one flesh."
Happyness wont come if they have different Religion..
Happyness comes when they are both content with what they have! I know there is always a urge for more.. But we must always be prayerful..
Lastly.. Couples must pray together..
There is a saying from where Im from! Couples that pray Together, stays Together!