Just for clarity, the train wreck does not describe the moral implications of the situation, but the fact that the TA has put a career, be it reputation or funding, at risk.
The information that I am aware of involves facts, such as explicit conversations and a visit to the apartment. It involves a history of a relationship beginning in a previous course and includes a compromising recommendation. The student signed up for the course on the TAs specific recommendation and signed up for the TAs section when there were multiple options. The professor does not know.
The university's policy states that there should be notification and that the teacher should remove him/herself from a position of authority. Very vague.
The reason for the post was not to involve conjecture or drama, but to find out specific experiences with this kind of situation-- academic dishonesty.