Definition of physical custody

In our seperation agreement it states that someone we are in a romantic relationship with may not spend the night under the same roof as the children when they have physical custody of them. I take that to mean on our custody days. My ex wife says it only applies to when she is physically there with the children. She wants to leave the children in her boyfriends care when she needs to travel and I think that is a violation of our agreement. Which one of us is correct?

I would need to review the language of the agreement in its entirety to give you an accurate assessment of the meaning, but you should also consider the spirit of the agreement. It is likely that the provision was meant to avoid the children being exposed to adult relationships, especially sexual in nature. Unless there is another provision giving you the right of first refusal to watch the children, it would seem she has the right to bring any third party in to supervise the children when she is not available to do so.