There are some things that simply should not be shared. For example, most wives object to a husband who decides that he should have a girl friend at the same time. The old-fashioned expectation of marriage is that two people decide that they will create an exclusive relationship that is unlike any other that they may have with anyone else.
That also means that your mother or father should not do anything for you that your husband or wife is expected to do. This may mean not feeding you when you visit in case you are not fed properly at home. It may also mean not allowing them to provide for your other needs which in the normal course of events would be provided by your spouse.
This can be quite subtle such as when a husband develops a friendship with a female colleague where they talk about things that they should only share with their wife. This kind of relationship may not include all the activities that a marriage would but it still sharing some things that are not designed to be shared.
Great harm can be caused to all concerned if these kinds of relationship are allowed to grow and develop. This is why some organisations insist that only people of the same gender work together as a team or if they do that they limit the amount of time that they spend together without witnesses. One being to make it look as if everything is done decently and in order to protect both the organisation and those working for it.