Yea in retrospect it feels like something could have been done, but i honestly dont think there really was--like you said, they couldn't have held either of them for long since the couple werent going to press charges against one another... they probably would have been separated for just as long as they were spending the night apart anyway. They didnt have any Reason to actually hold him at all (unless im missing something?)

There was enough to see that something was wrong--but i dont really think they could have reasonably predicted that someone's life was going to be soon in danger, just from what they saw in that stop, and definitely not enough to have intervened in a truly helpful way. You cant force people to accept help.