I've come to embrace the idea that the definition of strength is someone who can stand alone in life. Somebody who doesn't need to believe in a deity or a purpose for existence. Someone who doesn't need to socialize; to express their hurts, hopes, and emotions with others. That sort of thing is for people who are weak, and cannot be independent... right?
Or is the antithesis true? Are independent people actually weak? Are they too afraid to wear their hearts on their sleeves? Is what on the surface appears to be strength and fortitude just a facade to disguise the fact that a person is too afraid to show their faults?
I think that there are two different questions being asked here. So, let's take them one at a time.
Firstly, are people who do not believe in a god stronger? No, I don't necessarily think so; all of the strong Christians that I know do find great solace in their religion. Those who really do not believe, do not have that comfort. They are not necessarily stronger or weaker people, they just have to get on with things, without the belief that there is a divine being who is watching out for them.
The second question concerns whether those who do not confide their innermost feelings are weaker or stronger. Well, maybe this is similar to the god thing. However, all humans, being gregarious creatures, need an outlet from time to time. I don't think that strength or weakness can be defined, or measured, by whether you confide in friends or god. Some poeple are just unwilling to burden others with their troubles. Some of these people believe in a god—and I mean really believe—and can thus confide as if in a physical friend.
My position is broadly that I do not confide in friends; one often ends up becoming the pub bore. I am also a fairly private person, and would prefer that other people know as little about me as possible. I am also an atheist. However, I am also, generally, relatively laid back about things; what will be will be and something will turn up. Every now and again, I have a complete crisis of confidence in myself—as I did a couple of weeks ago. In my case, with nowhere else to turn, I yelled into the aether of cyberspace.
A few days afterwards, when the depression had subsided, I felt rather embarrassed (and almost more so at the flood of positive comments and emails)! However, all people need to get things off their chest every now and again; it simply depends on your method of doing it. Do you dripfeed the frustration out, or does it build up and blow like an emotional volcano? Do you tell friends or god or strangers?
Everyone is different: however, I still don't think that it has anything much to do with whether you are "strong" or not.