It keeps haunting you because you let it. You need to accept that he was obviously not going to go against his parents wishes and that all is not so bad since you HOPEFULLY learned a valuable life lesson wherein if you are ever with a guy that needs his parents approval as to who he can and cannot marry that you make sure, before you have sex or fall in love with him that you meet his parents and you find out if they approve of you.
Doing it any other way with someone who's culture and religion dictates that he marry who their parents must approve of or actually pick for him is just folly.
Time to let it go and get on with your life not even giving this another thought other then the lesson(s) learned not to be forgotten.
Give yourself the peace you are missing in your life.
“The willingness to accept responsibility for one’s own life is the source from which self-respect springs.” ~Joan Didion