My husband and I were in a similar situation when his ex moved out. We met about two months after she left him. After we were dating about a month I was around his children for the first time. I never stayed over when the children were there and I can understand you being upset, but children are actually more resilient than you might think. My husband’s children would not have had such a difficult time getting used to me and their father had it not been for their mother freaking out so often. In fact, the first time that she threatened me with physical harm was after the oldest told her that he saw me and his father kiss and it upset him. What he saw was just a peck and he had no problem with it at the time and even made a joke about it. His mother, while questioning about everything, two weeks later, got angry when he told her about it, which upset him so she called us to curse us because he was crying. She told me that I was not going to be around her children. This is very unrealistic and legally she had no say in who he had around the children as long as they weren’t in danger. The thing is the oldest wanted to get them together to talk, in hopes that they would get back together. After 6 months of this type of thing, he finally figured out that all they did after he told her stuff was fight and argue and quit telling her things. And when my husband started telling his ex some of the stuff that they told us about things that happened at their mother’s and we found out they were manipulating both of them. It was not as bad at her house as we suspected from what they told us and it was not as bad at our house as she thought from what they told her.
I’ll put it to you like this, talk to your children. Don’t put notions in their head, but find out how they feel about this situation. Don’t question them about what goes on, but let them know that they can talk to you. If they tell you things, keep it in perspective until you’ve had a chance to think about it. Keep in mind that the children are going to want you and your STBX to get back together, even if it was a terrible marriage, that is what the children are used to. After all, a bad situation that your comfortable in is better than a situation that is unknown and different, even if it is better. Children do not understand how much it may hurt or bother you to know that he’s moving on. They do not understand all the emotions that are mixed up with marriage and divorce. They don’t need to know all the details of the divorce either, since they don’t understand all this.
Talk to your STBX. Let him know that you do not want to know his business, but like it or not you and he are going to have to work together to get the children through this. That is the ONLY way it will go easier on the children is if as far as they go you and your STBX show a united front. Tell him that you do not care what he does when the children are not there, but that you do not want her spending the night while they are with him. This can be put into a separation agreement also. Trust that their father is not going to do anything to harm them, they are his children too. I know all this is difficult to see right now because things are too new, but it’s better that their father doesn’t hide that he’s seeing someone else. It’s better that everyone involved gets used to a new situation and will make it easier if/when you meet someone. If they are seeing either of you happy for the first time in however long you have been having problems, believe me, it is good for them.
Now, all that being said, when you do talk to your STBX, let him know that you hope, for the children’s sake this is not a long line of female friends that he is going to be dragging through your children’s lives. That is NOT good for them. They need to know that their parents are there for them no matter that they are not there for each other any longer. They need to know that their parents both love them even though they do not love each other any more. Keep that in mind when you meet someone also.
Sorry this is so long, I just thought that I should reply since I can relate to this situation and seeing it from a different perspective. Good luck to you and your children.