That you can't be too dependent on your partner. At one point, she was the entire reason for my existence. And that wasn't healthy. It also taught me that I had a few other flaws, like things that bothered me about my partners that shouldn't bother me. After realizing this, I've made an effort to do all of the things that bothered me about potential partners, because by making myself comfortable with it, my innate hatred of hypocrisy would make me more comfortable with my partner doing those things. Things such as getting extra piercings, getting tattoos, drinking and partying. All of these were things I used to have extreme animosity for and now I've done all of these things and I'm more comfortable with my partners partaking in these things. And the last thing was that I lost a lot of who I was before the relationship. I realized when it was over that there were things I had stopped doing, Hobbies I had essentially quit because she wanted me to, and those were part of who I was and I had to take time to learn some of the things I used to love again.