Obsessed with Cuckolding

I'm a student, living at home with my dad. My elder brother moved out a while back. A few months ago, mum left home for another guy, (she's had affairs in the past, but dad always accepted it) but since then dad has been looking almost obsessively at online cuckolding sites. He often forgets to log out, so I've been viewing his history. It's nearly always white women with black guys. (Mum's new man is from Nigeria.) I know he masturbates as he's looking online.
Recently, I told my boyfriend what I'd been seeing online, and he's become really keen on looking at the same sort of stuff with me, and likes me to talk about what we're watching. He enjoys watching me masturbate at the same time, and keeps asking if I'd like to do that with another guy. I have to admit the idea turns me on a lot. I'm curious about where this might lead, but I don't want to risk our relationship, as we've been together for two years.
I also know that my dad has discovered what I've been looking at, but hasn't said anything about it yet. I think more recently he's been deliberately leaving it open online.