Indeed - my dear Paul, the Police are simply not interested in a litany of character flaws. "Can we make a case?", in-essence, do the facts add up to illegality rather unwise conduct or impropriety and do the said events require caution, keeping an eye out, charging or whatever, is the only thing the CPS or the Procurator Fiscals up here care about. They don't want to arse-about on cases they can't prove unless the hypothesis is incredibly compelling and eventually Helen is going to start looking to at least one of them like the victim she is. Rob is digging himself a hole and by volunteering additional information at this stage as everything the Police take or record has to be made available to the Defence and this allows the Defence to and counter it as a direct result of a glorious thing call Discovery. Basically his goose is slightly cooked, it's just going to take a while to slow-roast him.... What a happy thought!
I would say he's afraid, he knows he's pushed Helen so far that she's prepared to do the previously unthinkable and that would terrify anybody. He's feeling vulnerable, weak, sick (the physical consequences would be ghastly) and every bully is a coward at heart and finds his own victimisation intolerable. I'll bet he knows enough to think she's got a few counter-claims her own, like being sexually assaulted and probably child abuse in the mental sense of the term, not to mention whatever Shula might choose to say and he reckons offense as the best form of offense.