I think you might be wise to think this one through a lot further.

1) It's a major breach in the trust that he has for you. Whilst I accept that it is a way of protecting yourself, you are landing him in massive amounts of trouble.

2) There is a risk for you however; the question that immediately would follow from his parents would be: 'Why did our son think this might be a possibility?' You would attract suspicion to yourself, and although you might be able to laugh it off, in practice it would constrain you for the future.

Which is why being very careful when and how you meet him is vital if you think there is a chance of this. And you might do worse than to think out an 'instant' response if the worse did happen; it would reflect a moment of great trust on his part, which it would be sad to crush. On the other hand, you need to block any prospect of a repeat. Not easy...