Thank you so much for sharing your experience. Honestly, the same situation can mean different things to different people. Trauma is subjective, the way we react to things is also subjective. For example, I'm terrified of spiders. If there was a tarantula wandering around in the supermarket (hypothetically), my reaction would be very different to somebody who, for instance, studies arachnids for a living.
I can see that this situation has affected you greatly. I used to hear it so often, that romantic relationships in your teenage years "don't count" or they "aren't important" because of your age/maturity but that's really not true at all. These experiences and the feelings that come from them can follow you for years afterwards. You're not overreacting at all, your feelings are perfectly valid. This friend who was talking badly about you to your ex also sounds toxic, I would consider removing her as a friend or at the very least, distancing yourself from her.
Maybe talking to a therapist or psychologist would help, just somebody to help you come to terms with your experience and pinpoint what moment or thought it was that has stayed with you for three years. It can be very therapeutic to get it all off your chest and have a non-biased third party listen to what you've got to say.
Also, acne's totally fine and very normal. We've all had it at some point. If it makes you feel any better, Kendall Jenner is one of the most renowned supermodels in the world, and she's struggled with recurrent acne through most of her career. It doesn't make her any less attractive, or any less of a model. It happens, it's natural, and it shouldn't be something to feel insecure about at all.
I hope you're doing well, and please let us know if you have anything else to say! We're here for you.
Kind regards, SB