I tried loving a girl but she didn accept my love! I am depressed. what can I do? should I quit or try another?

Few years back I was attracted by a girl and started loving her but when I said my love to her she didn't accept. I tried a lot but she didn't responded. I was so worried. I don't know what to do. One side of thought said me not to love again and get depressed again but other part said there are plenty more girls out there. so took the second choice. I started loving a girl. I was so much attracted because of her character. She was so admirable. I liked her very much but sadly I came to know that she was already dumped by her boyfriend once and she was from another religion. I didn't considered those things. I started loving her. I was a fat boy. She told me I look better if my body was fit. so went to gym for months and tried my best to keep it fit and I also studied well because she said so. Once she said that I will surely love you if you had came before my ex. I have missed you in my life! So I thought she was in love with me. One day i said I like you and I will be with you forever. It reminded her his ex boy friend. suddenly she said not to love her and not to do anything for her because his ex boy friend said the same words and cheated her. I was about to convert my religion for her and to speak to my parents about her. she said she will surely marry me if her parents accepts me. so I was about to speak to my parents about these things. but she suddenly said those things because of her ex boy friend. I don't know what to do. I tried to make her understand my love but her reply was please don't lie to me I will believe those lies and get cheated again. She said that she likes me and she is willing to marry me if her parents accepts me but she never said whether she loved me or not... I dont know what to do. I am so depressed. I did many things for her but suddenly she said not to do anything for her and not to marry her. she said If I marry her she would be an unnecessary burden to me. I dont know what to do. My brain says me to move on and my heart says me to stay for her. what should I do whether to move on or to make the girl understand my love. if so how can i make her understand? Or to forget the thought of loving another girl in my life and stay the same without loving anyone and giving up the thought of loving or off course moving on is a terrible pain. I am totally helpless. Life is once so i want to enjoy the joy of love. but as per my current situation I dont know what to do. Please someone help me!!!!!!PLz