First off, just a little background of myself. I grew up in Minnesota where I became a huge fan of Kevin Garnett. I then moved to Sacramento, California in third grade and lived there until 6th grade. I now live in London. As you can see, I have never lived in an area where the Celtics are widely supported. My fandom of the Celtics was inspired by Garnett. After being traded to the Celtics in 2007, all I wanted Garnett to do was win a championship. He was such a class act for Minnesota and I just wanted him to succeed. That is when I started following the Celtics.
Now residing in London, it is tough to be a fan of any NBA team. With a five hour time difference, I was forced to invest in NBA League Pass so I could watch games at suitable times. Games can start as late as 2:30 AM. This makes it incredibly tough to watch games.
One other negative besides not being able to watch games is no one is interested in the NBA anyway. Soccer is huge in England along with rugby and cricket. The British Basketball League (BBL) is so unpopular that courtside seats are sold for $7. The BBL is pretty pathetic and is well below Division I college basketball competition--garbage. No one is interested in the game over here and it is extremely rare to even find basketball hoops at the local parks.
In summary, being an NBA fan in London sucks. It is difficult to watch games, no one is interested and it is hard to even play yourself. My advice to you, if you love basketball stay in America.