Thank you for your question
My name is Clare
I shall do my best to help you but I need some further information first
How exactly do the children share their time between you?
Where do the children sleep
How much have you been paying towards the house your ex lives in?
How much is it worth and how much is outstanding on the mortgage?
Why are you the only one paying the childcare costs?
How much would a two bedroom property in the same general area cost to buy?
I do understand why you are doing this - but the simple fact is that you are causing yourself financial difficulty because you feel guilty that you chose to leave.
Do please stop.
You are sharing the physical care of the chidlren equally - and should be sharing their costs INCLUDING childcare equally as well.
He should be paying the mortgage PLUS half of the children's expenses - since you have the cost of renting.
If he cannot afford to remain in the property then he either needs to give you the chance to buy him out OR the property needs to be sold and you will both need to move on.
With regard to your new partner when your children are with you then you have full parental responsibility and the right to decide who the children do or do not meet (provided of course that the person in question is in no way a risk to them).
Your ex will NOT be able to change this -
I hope that this is of assistance please ask if you need further details