Should I have taken her back?

I dated this girl my senior year, and she was a grade below me. We dated for a year and a half, then I got back from college a little early, and by complete coincidence, I ran into her dropping off some other guy. As it turns out, her and 2 friends went to a haunted house (Holloween time) and one of her friends invited this other guy. So All I see is her and her female friend pull up with 2 random guys. Long story short, I blew up and we broke up. After a year and a half of dating, and about a month of on again off again dating, she starts dating this guy. They date for a while and then we started talking. They break up and we date again. We have been through a lot, it was a bitter break up and I almost killed this guy. I went downhill, developed a drug problem, all over this bullshit. I am fine now though, so no worries. But we never had sex or anything until we got back together, then we had sex within that week. And her “Oral skills” seemed like they improved. I don’t know if she was just really passionate after we got back together, or if she messed around with this jerkoff inbreed. She swears on her life she didnt mess around (except kissing) and I am not 100% sure if things will ever be like I know they could be. what should I do in this pickle. also, they only dated maybe 2.5 months or so.