Last time I checked, it is completely legal to videotape people in a public place, therefore, I don't see a problem with that.

Your daughter on the other hand? That could be an issue. Is he younger than you and is it his biological daughter? If he is younger than you and it isn't his biological daughter, then I would confront him about it and consider taking him to therapy, but not outright break up with him over it because it is biologically healthy and normal for men to be attracted to women younger than them.