It's not happiness. It's being trapped between two emotions - the joy of having and caring for kids, and the despair caused by constant drudgery without perspective. Some people manage to focus so hard on the former that they forget about the latter, at least for a moment. But others can't.

I'm struggling to see the connection here. You can love someone and still be unhappy. Abuse victims often love their abusers. Suicide victims often have loved ones.