Libraries and fast food restaurants are also viable places for pickup/dropoff of kids - basically anywhere that's a public space which has security guards.
I don't think there's anything you can do if he and his gf are across the street from your home, unless you have some sort of order that specifies a radius (i.e. neither of you can be within x metres of the other). However, this makes pickups/dropoffs difficult because you technically have to breach the order to carry them out. It is weird and unsettling, however.
I'm sorry you have to deal with this!