I actually think there are signs. He is seen to be simultaneously drawn to him and envious of him and also occasionally disgusted by him. But I think the rape is more a way of attempting to assert dominance. He thinks he owns him. His son behaves in a similar way towards the niece (and there's a hint of possible sexual assault there as well).

I don't think the Venice sequence felt particularly superfluous. It's too brief and after the events at the end of the previous sequence, felt like a well-judged breather.