What the hell should I do?

Me and my girlfriend broke up a couple weeks ago. She started acting all jealous and was getting pissed that i was hanging out with other girls so soon. I kept telling her that i didn't hook up with anyone or anything like that which is true. She came over this weekend and we worked things out and had an awesome time and she was saying how much she loved and missed me, but then before she left i saw some dude blowing up her phone wondering why she wasn't answering and said something like "im getting worried that my girlfriend hasn't answered me in a couple days". I questioned her about it and she said he was just some dude she knew when she was a kid and ran into him at work and had just been texting and bein friendly with him for the past few days and that she was getting the feeling he was into her but she never even hung out with him or anything. I broke up with her over it, and she was crying and pleading me not to, and swearing on her family and son that nothing happened with the guy and that there was nothing going on. She even sent him a text in front of me saying "i worked things out with my boyfriend and i dont want to give u the impression i want anything with you, sorry but im not interested" and then she blocked his number. She even got her mom to call me and tell me that she knew the guy and that there was nothing between them and that she had not been anywhere besides work and home, so there's no chance she could have been hanging out with anyone. I dont know what to do cuz i love her so much and dont want to break up but i also can't stand the thought that she mightve been with someone else. If i break up ill be heartbroken and if i stay with her, then ill be paranoid. I don't know what to do. Any advice would be very helpful.
What the hell should I do?
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