<human>: Can you summarize the given text in a few sentences?

I broke up with a girl about 4 years ago, we remained friends even though she started dating someone. After a year, she says that the relationship has ended and she's moving back home. We are best friends so we told each-other everything. Fast forward three years, she tells me on Friday the guy is still with her and has been living with her this whole time. She told me that she would tell me if she was ever in a relationship. I honestly don't know how to feel Reddit. I loved that girl with all I had. What did I do so wrong.
<bot>: My best friend and the girl of my dreams lied to me about being in a relationship while we were apart for 4 years.