First and only relationship, for 6 months before my 21st birthday. That's just under a year ago. I wasn't over her for probably a good 6 months - basically I went through a phase of wanting her to be unhappy and me to be happily with someone else (I broke up with her because she slept with her ex-bf) but now I'm just like "meh.." don't really care.
I'm sorry to say this, but I really think you should get rid of the letter. Sounds like you're clinging onto it because it's something that reminds you of her, but all it does it make you cry and hold you back. You can only live in the past for so long.