27 [M] with my fiancee [28/F] of three years. Found unflattering messages about me and I don't know what to think

I have always had a big crush on my fiancee. She was my sister's friend in HS (a grade ahead of me) and we both attended the same university. She and I were never close but definitely knew each other - she and my sister spent a lot of time together.
We started dating 3 years ago, she had come out of a tough relationship with a guy that everyone universally loathed. She stayed single for a while and through a bunch of random meet-ups and hanging out with my sister, we ended up getting together. I was thrilled from the start, we've had a really easy going courtship. She started hinting that she started to hint that she wanted an engagement and 6 months ago, I asked and she said yes.
Yesterday she has been changed her email over and asked me to go through old emails and forward anything I thought was important to her new account. She asked me because it's an incredibly boring task. So, I was going through and found emails from around the time we started dating and continuing to about ~4 months into our relationship that are between her and a friend that was living in NYC at the time. It goes into pretty solid detail about our relationship and comparing me & her ex.
The emails.... aren't flattering. At first she questions why we're together, then questions what we're doing together, compares me negatively to her ex and isn't sure about what she is doing in a relationship. The emails are pretty frequent for the four months when the subject abruptly changes to other things and she and her friend don't discuss it.
At the time, we talked about our feelings and she never voiced anything. Over the last three years, we've become close, she's told me that I'm her best friend, we've planned for the future. The emails really spooked me. They were also hurtful. I know they're in the past, but I just feel really crummy. I didn't mention them to her, I'm sure she forgot about them.
Should I drop it? Why do I feel so crappy?

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tl;dr found emails about me that were really unflattering, feel really low after reading them. Not sure what I should do after finding them, if I should just drop them, or if I should just leave it alone. Feel really low.


Source.