Respect, love and happiness are all the obvious vitals of a relationship. However, humour, sarcasm and the odd arguement keep it alive.
All these stem from good communication, if you can say anything to each other you're on for a winning combination.
I'm engaged and we are planning a wedding. I annoy the hell out of my fiancee but she knows I love her because I show it and there is no harm in telling them often how you feel.