If you guys are close you can always get your circle of close friends together have a couple of drinks and then usually around 3-4am when it settles just a bit have one of those calm serious conversations. If she really is psycho and he is love drunk then he may not see it now, but at least when he finally wakes up he will remember his friends tried to help him and didnt stop. Then again maybe with all his close friends in one place trying to tell him the same thing he will listen.
But then again, unfortunately sometimes they dont snap out of it and they settle down with that person and drift away from all their friends as a result. Ive seen that exact thing happen with two close friends, either they were love drunk or just stupid.