Going abroad, leaving loved ones for 4 months?

I am going abroad soon. 4 months volunteering in Nepal. I am leaving behind my boyfriend of two years and my family who I love. I am getting so nervous and I can't help but feel so guilty for leaving them. I feel like a bad person. I know I'm doing something great, but I'm scared to death. Has anyone volunteered abroad or went abroad for a while leaving your family? Any advice? Is my relationship going to be okay? I know he is faithful and I am, but I hope he doesn't overreact to me going. He knows I am, but he is getting stressed about it as well.