Just-Me. Your rant is actually the same rant that most of us who have gone through heart-break have and its okay - its healthy its glad you got it out. While you may say you don't love her anymore -- trust me you do...you are in the same state of mind I am/was in. The only and best thing you can do for yourself is to break off all ties from her. I have probably seen my ex once in the past month and I deleted her from facebook, deleted all the old emails, moved the pictures to an archive on the computer etc.. because I knew thats what I needed.
Its okay to feel like you wasted time, its okay to feel like she is an awful person -- in truth though shes not -- shes human, we fall into and out of love -- its the risk that all relationships take, that they won't work out. The only solace that I take is that we broke up now, before we moved in together, before we got engaged, before we got married etc...
HOPE is your number 1 enemy in all of this -- let it go -- my friends gave me this tough luv: she is not coming back, she is not going to realize her mistake, she is never going to learn her lesson. And frankly -- it should not matter to you if she does or doesn't. Take control over the only thing you can right now and its how you let her impact your life going forward, so take out your phone -- find the contact and hit delete, now repeat that for facebook, old emails you have been reading etc.. Facebook is evil when it comes to breakups -- the last thing you want to see is her status go from In a relationship with XXX(ME)XXX to Single and then to In a relationship with XX(DOUCEBAG)XX -- let it go. Take a breath.
As far as going out and having a one night stand -- I've been there and done it when heart broken in the past and for me it was awful -- because the whole time I kept thinking of the ex (not this one) and then when it was over I had to deal with the fact that I just used someone, and that person despite the fact that we were having a one night stand insinuated she wanted to see me again...I had no interest in seeing her so now I feel the guilt of having led her on. But -- it might work for you.
Some say dating is good -- some say it is bad and you should wait. I say as long as you are open with yourself and the person you are with that you are just looking for someone to spend some time with, then its okay -- and its a good way to eliminate the time that you are sitting at home dwelling.
Lastly, I don't know you and I've never seen you BUT -- YOU ARE attractive to girls, you attracted this one didn't you? Don't allow one person to make you doubt yourself and break your confidence, chin up! If you feel you need to lose some weight and it sounds like you already have -- hit the gym...it will make you feel better about yourself, undoubtedly improve your health and is just an all-around good thing to do. Got it? Good.
Hang in there.