Happiness is a by-product. You cannot pursue it by itself.
If you want to know how your girl will treat you after marriage just listen...
On a soap happiness never lasts for very long!
Whereas I used to get depressed or neurotic or dwell on things I see my son's bright eyes and smile in the morning and suddenly I don't feel like I'm depressed anymore. There's nothing to be depressed about when you've got that.