That blows but it happens. I was cheated on once. It sucked a lot and it took a bit to get over, but in time I got over it and just as said.. I feel stupid for even being upset, now I am just glad I moved on to a billion times better. Breaking up and being dumped are two things you can be on the end of and both hurt, I ve been on both ends and it sucks but you will feel much better as time goes on. Sometimes it takes a few or many tries. As said before its better you found out now instead of years later and just wasting more time with her. Now you can find someone who is better than her. Now you have an opportunity to go enjoy your self, try new stuff, talk to other girls and date - nothing serious and just have fun, there is so much out there to do. Go out on a trip with friends or something. None of this will take the pain away right now, but the pain will go away in time, but these things will help you move on and enjoy your life, instead of wasting time locked up in your room upset over an idiot girl. Getting out helped me a lot. As for burning stuff- do it!! It will feel good to burn all of that stuff - I ve don it before, its like a relief almost.
Oh and I wouldn't take her back ever, even if she regretted it. My first ex told me he regretted it... I told him not to talk to me ever again (super glad I did too). If she did it once I would say that is not someone to be in a trusting relationship with.