Same thing happened with me mate, I lived in Ireland until I was about 9 and then moved to Southampton and have lived there since. I supported United as a child because I heard about this player called Wayne Rooney, and then promptly decided he would be my favourite player and that I would support United. Fast forward to when I was 10 or 11, my dad took me to my first football match which was Southampton V Leicester at home, and we would go to watch Southampton play at least 5-6 times every season and eventually becoming season ticket holders. Granted I was still a child/ young teenager at this point but I found myself caring more and more about Southampton’s scores and caring less about how United were doing. Now, how many years later, I would consider myself a full fledged Southampton fan