I've been there. Like I said, I wish someone would have hit me with straight talk at the time. I might not have listened, but I also might have.

Good luck to you whatever you decide to do.

You know how it felt when you found out? Get used to that feeling.

There's zero chance she stops this behavior. And at this point you know this already, so your choices are: The pain of a breakup which will suck but eventually be over. Or the recurring pain of being cheated on until you're eventually cast aside...which gives you extra pain and then you get to go though the first option anyhow.

I'm sorry to put it so bluntly, but if someone had done that with me when I was about your age it would have saved me an incredible amount of heartache and the time it took to unwind some unhealthy defensive behaviors I developed.

I know working it out is viable for some people. I've never seen it work though. I'm 100% against any form of cheating and 100% against staying after such a thing has happened. I'm almost twice your age and have seen it with friends, experienced it, watched it happen publicly...the 1% chance that things will get better will not happen for you. rip the bandaid off. Deal with the suck. Find someone worth your time.

Good luck.