GLUE ON PAPER
Growing up I used to play a lot of sports. Every sport has an element of defense to prevent the other team from scoring. When learning to play defense in basketball, there was an element of following/covering someone constantly. Our coaches had some phrases for this kind of defense. They would, "Stay on him like:
This "glue on paper" is some of the language that Jesus references in Matthew 19:5-6.
Cleave
Jesus is being test by Pharisees about the proper conditions for divorce, and Jesus responds with: ‘For this reason a man will leave his father and mother and be united to his wife, and the two will become one flesh’[b]? 6 So they are no longer two, but one flesh. Therefore what God has joined together, let no one separate.”
"Be united" is also translated:
Bible dictionaries talk about this meaning "to be glued to."
Have you ever tried to separate two pieces of paper that were glued together? You can't without destroying the paper.
Wholeness
Jesus has this same kind of imagery in mind. For Jesus, the marriage union was such a uniting, joining, cleaving, gluing of two people together that the two people were indistinguishable moving foward - no longer two bodies of flesh, but one body of flesh. Anything/anyone that would divorce the union would do great harm to both parties.
I do want to note that certainly folks have found legitimate reasons for divorce in cases of infidelity or spousal abuse. However, many divorces in our day and age are due to:
Jesus would note that outside of situations like infidelity or spousal abuse, it's actually better for people, families, and societies if husband and wife to stay glued together, work on their marriage, build trust, and build intimacy. This is certainly the path to happy marriages - not ungluing two pieces of paper.