Have you ever heard the expression "weakness is a woman's hidden strength"?
As people, we tend to have no sympathy for the strong, but we sympathize for and pity the weak. We won't cut the strong any slack, and in fact, we'll feel more comfortable being harder & tougher on them. But we'll do exactly the opposite to the weak. We'll give them chances, we're not as hard or tough on them, we basically play favorites.
Growing up, boys are taught to be strong, and more importantly, to never show weakness. While growing up, girls are usually in their environment. Boys grow up next to girls who have no pressure to be strong, and no restrictions against being or "acting" weak.
One of the ways girls do this, is by "crying".
In fact, the tear ducts of boys and girls are very different. It's much easier for girls to turn on the water-works than it is for guys. So for guys, it takes a lot to cry. So when guys see crying, it implies some strong negative event (since that's what it would take to make a guy cry); but that's not necessary to make a girl cry. In fact, no strongly negative event is necessary for girls to cry. Many girls can simply "make themselves cry".
It gets to the point where when guys see girls crying, they feel it's "dishonest" & "manipulative".
But these are only feelings they feel when a girl is interacting with him (in other words, has incentive to lie, be dishonest & manipulative).. If the girl isn't interacting with him, or isn't in the position to get anything from him; then (HE), the guy, is in an emotional position to feel safe enough to sympathize and feel bad for that girl & what she's going through.
But if it's a girl that's close to him, like his wife or girlfriend; then the breaks of reason & logic jump in FIRST, BEFORE any information is passed along to any emotional process.. This explains why guys might appear "colder" or "less sympathetic" towards crying from their girlfriend, than say, crying from some totally random girl..