Bathing with dads girlfriend

My son just turned 3. My little one informed me the other day that he takes baths with the girlfriend and she has a “costume” on her peepee.

I said do you mean in the pool or the bathtub he said no the bathtub that’s white.

I messaged my sons dad and told him this is inappropriate and not ok he told me he’s “confused” they play in the kid pool together and not the bath...

I am pretty sure my three year old couldn’t make this up.

We’re going through a messy custody battle right now and wondering what to do?? Do I report this?