I'm going to attempt a hand written letter perhaps with a little parcel of things that mean something to both of us, photos etc
That sounds like a recipe for an ex-boyfriend bin bonfire.
Get your arse up there, and take her away for a night to talk things over with no-one else around. Tell her how you really feel about her, and if she really is "The One", beg, grovel, and make sure she knows you're not just doing it to fool her into taking you back.
If she really feels the same way about you, and is just pissed off about the breach of trust, she'll take you back. Otherwise I'm afraid you'll just have to accept that it's over, and find someone else. There's no point dragging a relationship on when one doesn't trust the other, as both will end up getting hurt.