I've recently come out of a 4 year relationship (on/off) with my best mate. Who I made the decision to cut out of my life completely now. It can work and did work for the most parts, but when it goes bad it goes seriously sh*t.
I don't recomend it for long term, but for fun it can be amazing. I guess its the whole "how much do you wanna invest?" question. Some people just click, but just because someone is a best friend doesnt mean they are viable as a partner, its a different ball game, you gotta make the transition. If you stay in the friendzone mindset when you're in a relationship, its NOT going to work. Obviously.