In addition, the fact that Marion told Sally that the man she saw in the car was 'a friend she met at the arts centre'. Sally thinks Marion had no reason to lie about it as she was always open about boyfriends.
Pure speculation, but I feel all this 'friend' stuff is leading somewhere... Eventually, RB is going to have to explain why Marion changed her name to the initials and surname he was using at the time. For this to work, he needs to have been romantically involved with Marion.
We already know his story is that they were lovers who reconnected. It will be easier to believe she changed her name to his if they were in love and it was a cute homage to him, or even that Marion was obsessed with him. I bet a millions bucks he'll say that Marion was obsessed with him and followed him overseas but she never found him and he ran away from her because she was a danger to him!
However, if there is evidence RB's MO is to befriend his victims, and the fact Marion said he was only a friend, his story may start to crumble. If they weren't lovers, she must've changed her name because he told her to, because he needed her to, such as for the purpose of withdrawing her money in the UK or whatever other fraud he had planned. Hope that makes sense.