Never ignore red flags
This piece of advice rings true with any relationship, sociopath or no sociopath. I wish I didn't turn a blind eye when she stopped coming home after work and started sleeping on a "co-worker's couch" to avoid the long commute home. I wish I called her out on messaging my ex-girlfriends on Facebook, and I sincerely wish I had dissuaded her from stealing from every single store we walked into.
That's the thing about these kinds of awful relationships: you just choose not to see the red flags, even when they're right in front of you. I remember asking her, via text, if she cheated on me. She said yes. I asked her if she had sex with the guy she cheated on me with, she said yes.
When I called her and told her it was over, she told me I had read her texts wrong… she was "saying 'yes' to two different questions.'" Which two questions did she think she was replying to? She forgot, of course.
I tell people that I moved from Boston to New York because there was no work for me in Boston. In the back of my mind, I quickly add, "Plus, I wanted to get away from my ex-girlfriend."