My birth father and older brother are reds and took me to Old Trafford for a season around 1987. Then, my parents separated and my Mum met who I now call my Dad who is a blue.
For a few months, each of my Dads would take me to watch whoever was at home.
There were a number of lads in school who "supported" two teams. One who liked United and Villa, one who liked United and Forest, one who liked United and Everton.
We were playing football one break time and one of my classmates picked up the ball and shouted everyone in. He said that we all needed to choose the team we would support forever and couldn't pick two teams.
We ended up with 2 Liverpool fans, 1 Everton, 1 Villa, the rest United. I was at the end of the line and just said "City".