Whats it mean when you're still not over your ex a year later?

I dated this girl for 4 months, we clicked so well that we would talk all day during work over email about nothing, and still have time to talk for hours on the phone and hang out all weekend at the bars. I had a nervous breakdown bc of a certain diagnosis and lost her by not thinking I loved her anymore (OCD is a bitch). Its been a year, and I STILL can’t get her out of my head. I just happened on all the emails that I saved….sigh. Any advice? I should also note that I’m 27 and she was my first true love.