<human>: Give me the gist of the text in a nutshell

During the time that I dated my last serious boyfriend, I got to know his family very well. I quickly took to his two younger cousins, but fell into an especially quick friendship with his younger sister, Erin. Erin was a few years younger than me, and very sweet and kind. When my ex-boyfriend broke up with me, I decided that in order to keep in contact with her since I go to college in another city and she's still in my hometown, I'd write her letters. We didn't talk enough to warrant online chatting, and I figured that it would be really nice to receive something tangible in the mail that showed her that I was still thinking and caring for her.   

I set out to write monthly letters/cards, and they were all on lovely stationary and decorations, with thoughtful and sentimental thoughts within. I told her about how college and classes were going, my journey to applying for Graduate school in English, and meeting a really nice guy (my now current boyfriend). I never got a message or letter in return, but I thought that as long as she enjoyed the letters and got a smile or two from them, that I didn't need a reply, and her happiness was enough. During cleaning up my apartment for the next semester, however, I misplaced the slip of paper that had her address on it. I ended up facebook messaging her today and asking her to clarify her address (was it 512 Xxxxxx Lane or Street?).  

**"Huh? It's 619..."** (pin drop)  

It took a few moments to sink in, but I just fucking realized that **I'VE BEEN SENDING REALLY CUTELY DECORATED, PERSONAL AS FUCK LETTERS TO A RANDOM-ASS PERSON IN LEAGUE CITY FOR SIX FUCKING MONTHS!**  

I'm so ashamed of myself. Some random-ass person has been reading my personal letters and I never worked up the courage to ask if Erin had ever received them. I would be mad at myself, but honestly, I can't even do that right now. I can only sit here and hang my head in shame.
<bot>: I've been mailing really detailed and beautifully decorated letters (meant for my ex's little sister) to the wrong address for almost half a year.