Fallen, Hurt, Heartbroken...Very Alone Please Help!

So...2 months ago I broke up with my girlfriend of 7 years. I have a hard time changing things and making critical decisions, but I was unhappy for about a year and realized she was why. Things started to look up the week before I broke up with my girlfriend (which I had already made the decision to do but was waiting until I had a day off) when one of my best friends (let's call her Mandy) revealed to me she had liked me for a couple years. She has always been incredible to me, and I myself have had feelings for her as well. She was going through a bad time in her life with her boyfriend (an ******) and confided in me. We hit it off. It was like a miracle. I have always viewed her as the perfect girl for me, and out-of-the-blue there she was.

Mandy broke up with her boyfriend on Thanksgiving. Things went from good to great. Until he kept coming around. Then she realized they were not done. Now they are back together. It hurts so bad, but I want her to be happy with or without me. The problem now is, we both have feelings for each other, but she loves him. She is now my only friend since the breakup. She is a good friend, and I could not ask for a better one. She listens, she cares, and she's fun to be around. The problem lies in my emotions. Then since she is my only friend I fear losing her due to me being too overbearing. If I cut her out of my life thought, things will get even worse. I will be completely alone, without someone I've loved for so long, and without my best friend.

Before the breakup I had about a dozen friends whom I hung out with, talked to, and was there for, but that has all changed. Slowly...one by one, each of them has removed themselves from my life and back into my ex's.

I have always been a happy person, outgoing, and fun, but for about month I have regressed into a horribly depressed state and have become very anxious. I go from extreme highs to extreme lows. I cry almost every day. I am just so lonely. I have tried reading, writing, movies, but nothing breaks it. I can't stop biting my nails (toenails as well as disgusted as that makes me), my self confidence has fallen completely, my diet is unhealthy, and I'm becoming bitter. I am fighting ambivalence towards Mandy. I am not missing my ex at all, I am actually relieved that's over. Its being alone that hurts so much.

Please help! I've never experienced this before. I'm broken, alone, and miserable.