I think there is always a nagging worry in a child's mind after mum and dad have split up...
... that mum or dad may meet someone else in the future. Children feel very protective of their parents and are generally not going to want someone to fill their absent mum or dads shoes. However, a younger child may be more accepting of having a ‘father figure’ around.
No-one can predict if and when this will happen. When it does, a child needs to understand that mum or dad have been feeling lonely and want to spend time with grown ups that they can talk to and have fun with. After all, the child has brothers, sisters and friends they can talk to and mum/dad need friends too. Mum/dad need someone they can talk to when they are in bed and sometimes they need a friend who they can share hobbies and interests with at the weekends when they are with their other parent. An explanation like this will be more accepting to a younger child but an older one may want to hear it like it is e.g. dad is no longer around, mum would like to have boyfriends and go out on dates, you don’t want her to grow old and not have anyone to share her life with, do you?.
Tell your child that you wouldn’t introduce them to someone you liked unless you felt sure they were ready to meet them and that just because mum/dad is going out for the night with them it does not mean that you are going to move them into the house you share or marry them.
Some children may guess that you have started going on dates as they sense something strange and different is happening with you and the way you are acting. Some parents try to make secretive phone calls and use code to talk about their ‘dating life’ when their children are around. If you feel your child would not understand about new friendships you are making then make and take phone calls when they are not around and only see your new friend/s when your child is with the other parent.
Many children who are not happy about their parent having new friendships will try and sabotage the new relationship by acting up and feigning illness so their parent cannot go out. They may feel that mum/dad is abandoning them and that they are no longer first in the pecking order. The chances are that your child is going to feel very strange about your new boy/girlfriend and worried about what it will mean about their own relationship with you and with your ex-partner. Children will often perceive the new person as a temporary measure and take comfort in this thought. No matter how important the new person in your life is, as a rule they are not going to make a tremendous effort or interest towards them. After all they were here first and they may feel that their needs, anxieties and feelings are being ignored.