I have found that best friends tend to come and go over the years as friendship depends on mutual needs and circumstance.
I've had several that I could fall back in with if the circumstances arise, but the most I do for now is an occasional email, Christmas card or beer when I'm in town.
First there are the best friends during school years that tend to change as you mature and become less naive to the world. You realise that some were not you're best friends after all.
Then you have best friends from tertiary studies etc who you bond with during that arduous and stressful experience of drinking, chasing woman, all whilst trying to pass tough exams.
When I enterred the workforce I met new best friends based on new locations, challenges and needs.
Some of the best friends that I have made have been during low times in my life when things haven't gone to plan or I am outside my comfort zone. I might find a new interest, sport etc, and very soon you have a new best friend in similar circumstances.
This forum is a perfect example of people who are new to Dubai and outside their comfort zone, making new friends.
Obviously everyone here is quite happy with their life at the moment and doesn't feel the need to be nice to anyone or make new friends.
At some point many people get married. They might have children which throw up many new challenges, priorities, and of course new friends.
However, I think once you become married and have children, it is inevitable that single best friends fall by the wayside. Your partner should be your best friend.
Those unlucky enough to end up in divorce meet a heap of new friends as they are thrust back into the singleton community. Two guys crying into their beers is the perfect catalyst for making a best friend.
When your partner dies, you are likely to meet many new friends at retirement homes and possibly re-marry.