Why can't i forget him? :(?

I simply cannot forget him. He is my first love, the first guy that I truly fell in love with and loved. Not a single day goes by without me thinking about him. It has been nearly a year since the breakup. I liked other guys, dated others...but I always think of him and my feelings have not changed. When I am with somebody new that I sort of like, it can take my mind off him...but only for a while. And at the end of the day, I am still missing him and literally ACHING for him. Sometimes, I feel like..."oh, there are other people out there. He is not the only man in the world after all." But I go back to missing him and feeling more brokenhearted than ever. He is with somebody else now, and he seems happy. But our breakup was very ambiguous...I feel no closure whatsoever. Is he my "true love?" He honestly made me feel like I was soaring, he was my EVERYTHING. Just seeing him was happiness, being with him was enough. It didn't matter what we were doing. Do you believe in soulmates? Is he the one guy I will always love, even if I get married and stuff? I feel like it is practically impossible to forget him...please share any stories, give me advice, tell me what do...:(