I'm glad @droughtquake brought 'the retired social worker' up, then I don't have to. But of course an old, single, gay man would never be allowed to foster two teenage boys. The evil dirty minds of people would make all kinds of wrong assumptions about that scenario.
I still think Robbie is better off keeping quiet about the assault for now, in spite of the obvious mental problems. if he could get some privacy to Skype with Tom, he might be able to tell him, once he's sworn him to secrecy. Oh, and his comment to Sue about not trusting her is fully justified IMO. Until she shows she's OK with Robbie being gay, she'll be in my black book.
As for running off to Florida with Alex, Robbie may toy with the idea, but I think he's too sensible and too scared of Alex to do it. But he could offer to give him plenty of money, if he goes on his own, without Luke. It would probably be much easier for the social worker to find a foster home for Luke without Alex. But Luke will of course be distraught at being abandoned.