The parents of the ill child will feel sorry for the child being so sick. They are parenting by guilt and give in to whatever the child wants to make the child feel better. The child then learns how to act a certain way to get what they want and the parents follow suit every time. In most cases, one parent is the main caregiver of the ill child and the other parent is left to care for the other children. The caregiving parent is constantly in fear of the child being safe and getting the care that they need. This leaves room for outside criticism of whether or not the caregiver is qualified enough to attend to the child, which leaves the caregiver feeling inadequate. It is also physically straining to care for an ill child. When having an ill child, the caregiver’s self-care is put on the back burner. When the caregiver does ask for help from the spouse or other members of the family, and they are not doing things correctly or cooperatively, this can cause resentment to the helping spouse or family member, which only draws the caregiver closer to the ill child and further away from the spouse or family members. It can also result in the caregiver resenting the child for putting the family in that situation.
This all would affect the marriage because one parent is having to focus on the ill child and the other parent is left to focus on everything else. If the parent not being the caregiver tries to help, the caregiving parent will just get mad at them and push them further away with each attempt. This can cause a communication problem in the marriage, which could be the wedge to start the downward spiral towards a divorce or infidelity. This could also affect the marriage because of jealousy of the time being spent with the ill child and not with the spouse. The caregiving parent could be spending all their time with the child and making sure that it is safe, while the spouse is begging for attention and not receiving it. This could bring up arguments, fighting, or even infidelity or divorce. Also, the caregiver could devote their life to the ill child and not pay attention to any of the others in the household, which means the other children are not getting love, support, and attention from that parent and only from the parent that is not the caregiver. This could cause a wedge in a marriage because the kids are unhappy with the caregiving parent and could influence the fighting and arguing between the parents and could lead to separation of the family.
There are a lot of ways a chronically ill child can affect a marriage, but I think that if the marriage and family is strong and has a strong bond and is willing to help out in the different dynamics of the family, the family could actually be okay and there might not be that big of an effect on the marriage.