Why are women and girls like this?

I'm a girl, and I think that men tend to have a more realistic perspective than women. For example: If a guy a guy thinks that having sex means having sex...where as women think of sex as getting married, being in love, having kids, being together forever, etc. Why is this? Women concoct this things in their mind and make simple gestures into being something they are not. If a guy says "Hey" to them, instead of that just being a normal greeting, they come up with 95840975340975 different things that it could mean. Why? I don't understand why they act this way.