[lederhosen]

I think it is quite easy. If you have a relationship with someone and having a "position of authority", the simple solution is to get rid of the "position of authority", let your lover have another boss. That responsibility is of course on the one with power.

I say "the simple solution" as it is the company policy of all companies I have been working for. I _guess_ it is the same for all universities.

I can _only_ guess that _maybe_ youngster is under pressure having sex with oldster with position of authority.

I need not guess that all these complexities could have been handled easily by assigning another professor to the student. And there is no question who's fault that is.

You do not need a contract, but do not fuck people that you have direct power over.