When a child is young, it needs to be respected that no one can take away, or replace their mum. Even if better in the long run for the child that the parents split, or get divorced, the long term effect on that child can never be foretold.
Every child will act and respond differently to their parents splitting up; some may see it as ‘great, I get two birthday and Christmas presents’ some may see it as ‘I don’t want to have to travel miles every weekend to see my other parent for only 48 hours’.
If the marriage is seriously affecting the child’s behaviour or mental state, then clearly the best choice is to go your separate ways. If the child is old enough to know what is going on, and is old enough to have their say, then that’s exactly what they need. Children will often feel at fault for their parents splitting, reassurance on the matter that it isn’t their fault is a really good step forward, and so is letting the child feel they have some say or control in the matter, otherwise the emotion of despair and worry will fill them to exploding point, another fiasco that could be avoided; there is no need for 3 broken hearts where two have already been split.
If you consider dating someone new, or even remarrying if you are at that stage, you definitely need to run it past the child first, once again making them feel like they have a say in the situation at hand. If the child reacts badly and hates the idea, reassure them by saying that you aren’t trying to replace the other parent, but simply meeting a new person, that may one day be your partner, not necessarily a parent to that child.
You can never replace someone when they are taken away, that is inevitable; but when you bring some one new forth, you need to put yourself into that situation at the age of your child, and gage how you would feel. If you feel heartbroken, betrayed, or aggressive towards the new partner, figure out why. Maybe you are showing off in front of the child, or maybe simply touching the person too much, sending a clear signal to the child that you are trying to replace the other half.
There is no way you can escape making jealousy for your child, at some point they will be filled to the point of exploding by it, it may not even be your fault, maybe you have just mentioned it and they have already expelled it out of the question. In that scenario make sure the child knows where they stand, with you and with your new partner, also let them know that your relationship wont change with them because of the new person, they already feel heartbroken that their parents have split, you don’t want to mix jealousy into the already explosive mixture.