my story

[Painter]

Personally, I would probably have been honest but dispassionate:

"I am very conflicted about this because I think it would be best for our children to spend as much time as possible with both of us, especially to help them feel that they are a priority to us in this time of upheaval for our family, but I don't think it's good for them to be exposed to your living situation with your lover staying at your place, because I don't want them to think that it's a normal or acceptable situation that I approve of. Do you have any suggestion to how this can be resolved?"

I don't know if this is in sync with DB or if it will be effective. It might not help resolve the issue, but it's stating a boundary that is important to you - and would be, to many.

Beware that percentage of time spent with each parent routinely for a period of 6 months or more can be used in court to modify a custody split. Which again modifies child support...