I have seen parents cause "chaos" over the years by handling issues like this inaproprietly.
Remember..."contact" is the right of the child not that of parents
Stop and always consider before acting....
"Am I doing this for me or my children"
An example of this is when a father demands overnight staying contact with a very young child-there are times when a build up to allow bonding etc is required.
Now the dynamics can often be observed as follows:
The Primary Carer starts to dictate to the absent partner contact terms etc.
In the old days when one party got custody many experts felt having such order and piece of paper did not helpas on occasions it would be used to dictate terms re access (contact).
Gladly those dark days are gone and in marriage BOTH parents have equal rights as they have "Parental Responsibility".
Responsibility as parenthood is a heavy burden as needs to be exercised in the children's best interests wisely.
Also the "wronged" party will be upset, bitter, vengeful etc so there are also difficulties of making clear and balanced descisions whilst in this frame of mind.
Many a contact dispute could have been avoided by either party having counselling...if nothing more than to step back and look at the bigger picture.
Remember adultery is often a sympton NOT a cause.
So where does all this fit in.
Both parents have to have the "bottle" to put their own person agenda, to one side in the Children's best interests.
If that means not introducing a new partner for a time to adjust then so be it. Too early introduction can be very damaging.
Children also will tell parents what they want to hear -so remember that...
occasionally they can play one off against the other.
As a rule of thumb a safe approach is not to introduce the partner unless the relationship is a stable one. Clearly if the parties are living together it would be an artificial step to keep the C away.....so start a gradual build up...with both parents reassuring the C of their love. I reckon after a 6 month relationship with no obvious problems is a useful guide but individual cases can demand a longer period if the C display such need.
There will only be one MUM and one DAD.
Sure there will be fears of a "new family" threatening the family unit but in reality this is a very rare event.
One word of caution - I have observed many teen girls ultimately reject a primary caring mother who has kept Dad away for years -when she grows up and becomes more mature..often when Mum may be in a new relationship and the Child's nose is out of joint...ultimately the unkindest cut for her.
Parents have to work TOGETHER and despite the hurt etc make joint descisions and back each other up so the C have direction.
Children love routine.
Contact is an adult descision and really children should not shoulder the emotional burden of such decisions. Court will if nec listen to girls at say 8-9 and boys a littlr older say 10.
You need to start talking with your Ex for to have a sensible relationship for the C must endure for years.
Consider "
mediation" if necessary.