GIRLS WHAT DO I DO ABOUT THIS GIRL? SO LOVESICK?

My answer may seem short after reading you long question but she sounds like a slut. You clearly deserve better and will find it but after 15 months its going to take time and patience. Just DON'T GO BACK to sleeping with her, otherwise you'll be starting from where you did before and it will take longer to get over her. You've also done the right thing by ignoring her after she was even more of a *****, keep it up. Good luck!