Wow... handwritten letters... in this day and age. This is SO romantic... unbelievable. Please keep the letters, scan them, and digitize them in order to preserve them - I have lost all the handwritten letters ever written to me by various guys (back in the time when handwriting was the default rather than a conscious choice) and I deeply regret being so disorganized. So the first thing is to scan, digitize, and preserve the letters.

Next, I would upload the scans into Google Drive which can then use OCR (optical character recognition) to convert them into documents that you can edit.

About Optical Character Recognition in Google Drive - Google Drive Help

So that would be my first step if I were you, because the attraction and attachment you have for this girl are clearly serious, clearly important (given the time elapsed since age 11...) and might well prove unique, in some sense, for your whole lifetime, so whatever happens right now in practical terms may be irrelevant for you three decades from now, but the handwritten letters will retain their relevance and will be precious keepsakes.

I am leaving for the long weekend and will come back to offer short-term suggestions; right now I just want to offer you some perspective and suggest that you invest time in the digitization of your handwritten archive.

And no, your novel is not pathetic - you write quite well and present the situation clearly and concisely.

Good luck!