very sad story, but it's bad  for you to remain sad all the time. The person who could not become yours and only yours is not yours anymore. Don't you think that the person is the betrayer of your life and hopes you built up with him for whatever reason?

He might have been in fake love with you so just furniced you a reason being his parents (caste if it was not the same between two of you, economic condition, education, beauty, or whatever, might be also be the hidden reasons) for going for another girl when he finally found a girl of his choice. See he could revolt against his parents decision easily, or he could just convince his parents that he was not yet ready to get married with anyone and hence come back to you easily if he was really in love with you. But he did not. So you need to think and move forward. You need to keep all of your hopes and aims of your life alive, live your life, try to be happy at the moment, because you are living not only for you, but for your parents, family and everyone. Your family's happiness lies in your happiness. Do not get frustrated and become lifeless too much. I hope you have strengths to overcome this difficulty. Good luck!

(It may be a great way to release suffocation, depression, feeling by sharing with others, so you might be sharing your story with us using Sajha. But, I think it is better to not to think much about your past and keep posting in Sajha monotonously. Instead better to go and mingle with your friends for some time keeping your study aside even when you have exams, or go for a roadside trip or a park with friend. You will be healed faster I guess.)