Ex-Husband popping up during your weekend with kids

Hey there!

Recently divorced here. I have custody of the kids and he’s the visitation parent. Prior to divorce he NEVER attended church. There are plenty of churches in the area... but he’s choosing to attend mine. He will even sit with me and the girls, we look like one happy family... I feel some kind of way about it. When he has the kids I don’t butt in: I value their father-daughter time. On one hand I don’t want to be that Christian telling another person to stay away and not attend... which wouldn’t work anyway because that would only encourage him to keep coming. On the other hand I strongly feel that if it’s his weekend I stay out of the way and vice versa. If it’s a school event and his weekend I’ll attend but I certainly do not sit next to him! Am I wrong to feel the way I feel? I haven’t started dating anyone yet but imagine if I was 😣