Caught! Sister's boyfriend ...

Now that's a tough one! Caught out cold and really embarrassing! My sister's boyfriend is watching my porn and as if that wasn't enough, he's also wanking with relish. I was completely flabbergasted, where can you find something like that? What do I do now, how should I react? What if my sister turns up again? This is a really tricky situation. Why is he putting me in this situation? Let's see what we make of it - do you think I've done the right thing?