Girls are trusting because of the way they were raised. If a baby boy cries, his cries are attended to far less often and less quickly than those of a baby girl. What you teach a baby boy with this kind of reinforcement is that his feelings don't matter. The he can cry and nobody will care, and that's mostly true for our society. On the same note, by responding to a baby girl's cries so quickly, you're teaching her that if she summons comfort, it will be there for her. That all she has to do is communicate what she wants and she'll have it.
This, among many other psychological factors, are why women are more social and men are more solitary. Women define themselves based on their relationships with others, men define themselves based on the things they do in life.
Everyone is psychologically indoctrinated, but women have more of it coming at them than anyone else, and sadly, most of them don't even seem to be aware of it. They're so caught up in the system. Lost in a maze of relationships.