I am so frequently asked about the best way to introduce a new partner to your child after divorce. There is no perfect way, but there are guidelines that can make the introduction easier.
Children of divorce have experienced loss. When their parents split up, even if they have joint custody and see both parents on a regular basis, they experience a loss of the intact nuclear family. That does not mean that they can't adjust to living in two households, but it generally takes some time and work on the parent's part to help them feel comfortable. Meeting a new partner can be complicated. A child may feel a loyalty conflict between the new partner and the other parent. It is important to help the child feel comfortable with positive feelings for both. It is not an either/or situation.
The first "rule" about introducing a new partner is that it not be too soon after the marital separation.The general rule is that a parent should be dating the new person for at least six or eight months after the separation and feel like they are in a new committed relationship (one that will hopefully last) before they even think about introducing the new partner to the child. The reason for this is quite simple: If a person starts dating someone new and is crazy about that person in the beginning, the feelings may wane in a few months, and they may decide that the person isn't actually "the one" and may end it.
If the parent has already introduced the child to him or her and the child becomes attached to this new person, when the couple breaks up, the child will again experience a loss. And this new loss will be compounded as it will re-kindle the feelings of loss from the marital separation.
If a new relationship is solid, and has some duration, the suggestion is that the new person be introduced slowly and to not just start sleeping over. Ideally, the child meets the person for lunch or dinner or in the park. And this can happen a few times as they begin to get to know one another. Then the new person can come over and spend part of a day on a weekend (and goes home before bedtime). Then gradually, the person spends more and more time until the child is comfortable and can slowly connect to the new partner. It is important that the parent pay attention to the child when the new partner is around, so the child does not feel replaced. After a period of time, based on the child's comfort level, the new partner can spend the night when the child is in residence.
Different children adjust differently. Some children are more resilient and can easily accept someone new, others have a harder time. It can be helpful if both parents are open to each other dating and easy with the child about it. If the other parent expresses jealousy or anxiety, the child will feel it and react. If the other parent is able to say something like, "I know your dad is happy with Mary and I think that's great," the child will be more relaxed and open to Mary. This attitude will ultimately benefit both parents.
If your child is having a hard time with a new partner, it is advised not to push someone new on him or her, and to consult a child specialist to strategize the best ways to help your child adjust to your new situation.