“I’m sorry, I’m know your wrong. I know a famous true story where a yichud with his fiancee caused a chosson (who’s a famous rosh yeshiva today) to almost jump off of a train. “
And that would have made it right – Yichud (not mamesh arayos)versus potentially committing suicide? Even the Torah does not say a boy and girl who have been intimate together are chayav misah (unless she was an arusah or an eishes ish). To the contrary, he is supposed to marry her. And that IS mamesh arayos.