When to make the two worlds collide
One of the hardest thing for every single parent is when they are dating someone and that faithful moment comes when they need to introduce their new partner to their children. It is a crucial moment in your life and you need to be extra careful about playing it right.
First of all, you need to make sure that this relationship is going somewhere as it would be unfair both to yourself, to your child, and even to the other person in the relationship if you introduce them when you know it is a dead-end. Plus, your child can feel if you are really committed, do not forget that.
Secondly, once you do introduce your child to that someone, you need to keep in mind that your child might feel that you are abandoning it for the sake of someone other than them and you need to ease their fears. However, you must not let the child to run the game. Your choice of a partner does not have to be under their direct control.
When it comes to the actual introduction, it is best if it is done during playtime or something like that. Also do not suddenly change your personality as it might confuse the child, making it apprehensive.