What should he do?

I don't know about the traditions in your area. But if I was the guy, I would probably just let go of the girl because it's obvious that she doesn't love him the way he loves her. Remember she easily decided to marry someone after 4months while they were with each other for several years. This just shows that the girl is unstable in decisions. Further, why settle with someone who has hurt you and whom your parents doesn't approve of if you could well find someone else better and who would not cause problems with family-members? But all-in-all, it's about the decision of the guy. Indeed love has a way to make us not see the bad things in a person. But eventually, he would see the wrong things and let's just hope that he loves her that much to accept those things. If I were your co-teacher. I would tell the guy to give it more thought. It's tough to be involved in troubles like these and I'm assuming he's still young, he could do a lot of things with his life instead of just settling right now right away. Remember, the girl has already made the mistake of settling too fast, what would make their relationship different? Let him spread his wings and find his place in life first. If she really loves him, she would wait - no matter how long.