Separation/Dating

I am separated from my husband. I have a new boyfriend. We are serious and I have introduced him to my children. My ex feels it is not the appropriate time, but this man is not a fling and I have not introduced my children to any other man. He also sleeps over occasionally. My ex is threatening to take my 50% custody away from me by telling me I am unfit to allow a man to sleep over. Should I be concerned or is this not really anything to worry about? I met this man after I moved out. Frankly, I think he has a bruised ego and is lashing out.

Other background, I left my husband because he had an affair. I only have proof of one affair. I washed the woman’s panties in with my own and he admitted it in emails to me which I have saved. He had a history of other inappropriate behavior during our marriage. I have introduced this man as nothing more than my friend, not even addressed him as a boyfriend. Obviously, I need to get a lawyer but in the interim will the court really take away my children?

Your ex may try and have custody changed based on your new boyfriend and the sleeping arrangements. To modify custody the movant must demonstrate there has been a substantial change in circumstances affecting the welfare of the children.
In my opinion your ex does not have a good basis to make such a motion, unless your new partner is a danger to the children, but I cannot speak to the attitudes of the judges in your county.
His affair is not relevant as related to what he is trying to do now.