How do I get over this?

I'm 16 and like an idiot I had gotten into a relationship with a 20 year old. I'm turning 17 though so we're only 3 years apart. He's also my coworker (his position is above mine though). Well he's a verrrry good sweet talker and if anyone ever met him they would totally instantly like him. 2 months into it, I find out from my coworkers that not only does he have a girlfriend.. he proposed to her so that makes her his fiance. I was so confused when I found out.. hurt.. I admit that I cried.. until the moment I found out she was someone I knew.. She worked with us also and had a higher position than his and is actually a year older than him. They have been together for a year and kept THEIR relationship a secret. I had NO IDEA whatsoever. That's when I stopped crying and my coworkers got me to tell her everything.. the whole truth to her face and as I was telling her everything that went on.. she was just twirling her engagement ring and writing him a letter. I heard later on that she kicked him out of what is HER house that they were living in. And the nice car he drove ME in was HERS! (I had never been inside "his" house so I never knew). Pathetically.. she was too weak and she got back with him less than 2 weeks later. Now all I see is them walking around together.. being the only person at work knowing the truth. Doesn't matter because I am going to quit soon anyways.. but I think.. I'm probably scarred for the rest of my life. I heard that I'm like.. the 4th person he's cheated in her with and the way she got back with him so quickly shows just how manipulative a guy can be. He probably bad mouthed me so bad to get her on his side. How do I get over this? Why are some guys.. ANY guys.. how can they just play with other people's emotions and hope they get away with it? I can't talk to any of my regular school friends who knows about this because I put up a fake front to act like I'm completely over everything that happened to me this summer.. but it's hard and I can't right now. I feel so scarred.. everything he said was a lie and like a complete idiot I believed. Every guy I meet now, I'm paranoid around. How do I get over this?