This question is invalid on its face. It assumes that every woman who hangs primarily around men is identical or has identical reasons for doing so. A lot of people in this thread have taken their own experiences and extrapolated them into more general trends, which is fallacious.
Worse, some people in this thread have taken their own behavior and extraoplated it into a more general trend. Given how much of a sausage fest this thread is (you could look around for twenty minutes and the closest thing you'd find to a woman is the poster who have female avatars) I shouldn't have to explain how fallacious that is.
Every woman is different. You can't pretend that all women will behave a certain way. It doesn't work like that.
My wife has had mostly guy friends her entire life, but I do not see this as a reason to distrust her. Her itnerests (the interests that lead us to get married, natch) are almost exclusively masculine when approached from her cultural background. Who the Hell else was she going to talk about video games with? Distrusting my wife for this reason would be indicative of mental deficiency on my part, a need for security so exaggerated that I'd be forced to doubt my own intentions.
Say you know a girl named Sue. Sue is a sexually open and active woman who is comfortable with herself and her partners and has no qualms about exploring different facets of her sexuality with different people. Is there anything wrong with Sue? No. Does that mean you should feel secure in a monogamous relationship with Sue? Hell no. Monogamous relationships are not what Sue is into, and if you go into a relationship with her looking for that then you are clearly presuming too much about your own importance to this woman (it's another thing altogether if she tells you she wants to be monogamous with you, of course, but that is neither here nor there).
Let's pretend this girl your'e talking about is named Jane. Jane is neither my wife nor the imaginary Sue. She is a unique person with her own sexual needs and expectations who behaves according to those needs and expectations. Jane has a lot of guy friends. You wonder if she might be having sex with some of them!
In a word, you don't trust Jane.
You have two options.
1. Talk to Jane about it in a thoughtful way that outlines your own boundaries and expectations concerning your relationship and encourage honesty on her part because you will not be judgmental, regardless of whether or not her needs are the same as yours.
2. Don't go out with Jane.
This shit is really simple
