resources: "Love Needs Laughts" https://www.youtube.com/watch?v=4qfum5vc4Ew
around 5:07 / 5:29
tips: this video has subtitles.
This means that to make something sound good, you can bend or break the rules.
There is a common phrase used at the end of children's stories. In the story the prince and princess have got married, and the story ends with the line
"they lived happily ever after."
The word "laughter" rhymes with "after" so this recalls the familiar expression from children's stories and links happiness (in your relationships) with laughter. It would not be considered correct grammar in formal English.