This is so confusing Leanne says that she likes her sexual relationship with Julian, but yet she still keeps her relationship with Tobey. I mean on this same episode while the family was away she called him to come over and that she was wearing a swimsuit in a flirtatious tone, yeah that shouts "hook up".
For the same reason that Julian has a relationship with Vera: at this point, Julian and Leanne’s relationship is about pleasure, about feeling good even when is twisted while their relationship with Vera and Tobey is more about having something more normal, funtional
