Most Helpful Girl
I say write it all out, absolutely everything you need to say and how you feel then store it somewhere safe, in a month re-read it when you are in a good mood, you will realise that you shouldn't send it because you sound stupid and hopeless, when you're not.
I did this, I wrote a long email to my ex and sent it to him, then the next week I hacked his email just to delete it because I realised I sounded pathetic. Luckily it wasn't read.
If you don't want a future with your ex (the guy who he is now, not the guy he used to be) then what's the point?
Leave it and you will get over it eventually. Promise.