I need help with dealing with heartbreak and rebound issues..?

I have been deeply in love with my Nad for over 3 years, and have been seeing her for every day throughout our relationship. All was perfect between us, and my family even proposed to her. However, the only problem was that she was 3 years older to me, and based on that factor, I was rejected by her family, and now she is in another country. Its been a month since we split, and the pain is still there. I know i need to move on, but its just too painful to see it through. I am a reclusive person now, and the only person whom i m close with is Nad's sister, who is living nearby. She already has a bf. Tho i am not in love with her, i m scared that my vulnerability and her affection mite lead me to fall for her. But i do not want to lose our friendship, coz thats all i have left to hang on to...I need help...please advise me on hw to cope with heartbreak and how to prevent from falling in love again...