I draw for my clients first an oval with a stick figure inside. The oval represents their independent sphere or domain. Inside of the boundaries of the oval they are responsible for all things independent like eating, hygiene, work, friends, hobbies, sleep and more. A small baby can then be drawn in the stick figures arms to represent the absolute dependence of the baby on the parent for eating, sleep, clothes, and shelter.
Hopefully as an independent being we meet and marry another independent being, but what happens when you unite? Do the circles overlap? If that's what you thought, then you have just become enmeshed. Who is responsible for what now?
If the circles overlap on one another then who is responsible for how much you eat? Can you blame your spouse if you overeat or oversleep or dress poorly? Yes, you could, but it would be an unhealthy codependence.
Both partners would be dependent upon one another emotionally. Emotions should be kept within independent domains. They can be discussed and supported, but only the independent person can actually heal or process his or her own emotions.
Even if I accidentally pushed a person down the stairs and begged their forgiveness I could not heal them. Similarly if someone is emotionally hurt I cannot heal their hurt.
I draw a healthy marriage as two independent ovals inside of a larger oval that expands their domains. Within the larger oval they share childcare, house chores, vacation decisions, bills and money, sex, and many other things.
A critical task for all couples is to differentiate what tasks are individual independent tasks, and which are interdependent tasks that need discussed and negotiated.
Let me know what questions you have about this. I usually go on and on about this model because I like it so much!