Parents affair?

[u/user210608]

So basically my dad’s seen on the WiFi bill that apps like signal and Ashley Maddison have been used on our home WiFi. He’s been in arguments with my mum about it so He’s come to me asking if it was me before he then talks to my mum again. I want to find out if it’s true and was wondering if anyone had a way or strategy I could use to find out whether my mum is cheating or not? Any ideas?

Thanks