The first question I have in my mind is when you say "controlling people" what do you mean? yes I know what it typically mans to most people but in your case I am curious as to how you are defining these people and what behavior it is that you are trying to avoid/get away from?

Thing is, people who are overbearing and try to exert power over others do typically pick people they find have personalities that tend to give in and allow this type of behavior. Of course they can't know this about the other person but they gravitate towards those that seem to be the type that would accommodate their need for control.

The best way IMO to avoid such people is to work on how you interact with others, analyze self and figure out what it is that makes you attractive to the domineering types and find out what it is that you can do differently to attract different types of people. Of course it goes without saying that you need to understand how to discern those that can become the controlling type so you can walk away before it's too late.

I dont' think that over time that these people become controlling like you say, I think they are that way from the beginning and you tolerate it at first because they are enjoyable to be around for other reasons. When the entertainment factor of the relationship goes a little cold, all you're left with is a tepid relationship with a person that is controlling. Being more proactive in the beginning and paying attention to what you gravitate towards from the beginning will help too. If you want to stay away from controlling people, you need to nip it in the bud as it were. This is not all on them but on you partially too, after all you accepted the friendship and as I said, I doubt that their controlling behaviors emerge later, they just become intolerable later.