Yup, I agree with everything everybody has said. For me, it was a reminder of what I lost because I was a shitty boyfriend. I still have a box of those things, both the good notes and stuff, and the bad letters when things started going downhill. You'll stumble across it later and by then it will hopefully remind you of the better times and then you will know if you want to keep it or not. You guys could reconcile too, and you'd be losing some serious memories. Don't blatantly leave it out though, that will make it really painful.
To tell you the truth, I started forgetting I had it until I read this thread and it jogged my memory. You will eventually feel the same way.
Waking up next to a beautiful girl,
Step outside and say hello to my beautiful world.