Anxiety Attacks. Not helping that much.

My gf left me recently and in a few days time she is with someone else. I have known her for quite some time and she was my best friend too. The thought of her being with someone else is killing me. She is studying somewhere else. I know at this age these things shouldnt bother me but I really cant help it. Even while distracting myself I think about her and I am very scared about myself and how will I cope in the coming days/weeks. I really hate this heart sinking feeling and it brings tears to my eyes. I have never felt like this and I am not able to stay calm at all. I am almost 22 years old, and I feel ashamed of behaving this way at such an age. Ive tried talking to friends and family but its not helping that much.