Still cant get over an ex I know is wrong for me

I’m a 23 yr old guy. I haven’t been in any type of serious relationship ever since my ex of about 3 years and I broke up in college…ever since then I’ve gone from girl to girl and I usually have one night stands. I’ve been happy for the most part because I’m never the one that gets hurt and I love being able to do whatever I want without worrying about what my significant other is doing. however, about 5 months ago I met this drop dead gorgeous girl through my younger sister and we hit it off like no other. she was rough around the edges and a bit abrasive, but I liked it because I was always into goody goody type girls. anyway, my sister warned me she was a little crazy and liked to party a lot and told me not to get involved with her because shes a heartbreaker…well, of course I didnt listen and I went out with this girl. anyway, she liked me so much…so much she would txt and call me all day long…funny thing is that I usually would get turned off by this but for some reason I liked it and the more we hung out the more I fell…usually im on the defense because I got hurt in my last relationship but this time I was so confident she loved me that I let my guard down. I even neglected the fact that she was a borderline alcoholic, had what I think is some type of bipolar disorder, and is regarded as being extremely promiscuous!!!…but she would tell me things like “you’re perfect” and “I’ve never felt this way about anyone” and we had some of the best, most exciting and intimate moments of my life … within 2 months we were saying “I love you” and everything was actually great… One night we even acknowledged the fact that she had problems and she told me that I was one of the good things in her life that was helping her overcome them and that she needed me. Her family even loved me like a son! then…she went back to college for her last semester and called me one day after she had been acting strange and told me that she rushed into the relationship and wanted to break up. I asked her why and she just kept telling me that I was great but she didnt want to be with anyone and wanted to enjoy her last semester. I was shocked. I even called her mom after and she couldnt believe it either…a few days later I found out from my sister that my ex met another guy and realized that she couldnt be with just one person. well, its been 3 months and I’m somehow worse with no sign of ever getting over this girl…apparently shes been with about 3 different guys since me…my sister told me that I was the only guy that my ex has ever been serious with and she truly cared about me but told me to just move on because she’ll never change. I’ve come to the realization that this girl is not right for me and I’ve tried literally every piece of “getting over your ex” advice out there…nothing is working and I think about this girl every day. can anyone out there help me???