Generally it takes a long time of hardship to maintain a teenage relationship to a good ending. There are just too many factors at work that can de-rail a relationship at such a young age. Money, studies, NS, maturity, parent relationship etc etc.
From my own observation of 10 teenage relationship I only saw 2 success cases. They know each other from Sec 4 until they graduate from Uni and get married is a total of 10+ years. That is what I called teenage relationship progress to hubby and wife ending.
So in general, teenage relationship don't last long and it is law of nature at work I guess
