Yes (a day or two late getting to this thread). you seem to have got the major clues. Slow down !
Rider is experiencing very understandable, natural fear. It doesn't mean he can't handle it but it DOES mean he needs to take it in manageable doses.
I might also mention that the best thing that might help - and speed the process - would be if he and "E" could get to know each other better. We fear most what we don't know ! Even if a deep friendship is not in the making between them, having a certain comfort level with understanding where each is coming from is imperative ! Knowing that they both have you as the center of good intent and that peace & happiness at home is also central to that will go a long way towards coming up with some guidelines and sensitivities that smooth out the ripples.
No substitute for common sense in these affairs - right ?