The Five Year Itch is that point where you know that it's more fun to play the field, but you don't want to let go of what you have -- and OMG, seven years is way too long. (Maybe its rly a three year itch)!
"Hey man, after five years on this fukin job and the same five damn years with the same girl, I'm itchin bad, and it's not a shot of antibiotics I need."
"Five year itch, bud", said Greg. "What you need, is some variety in your life.