I was a toxic boyfriend. I used my ex for years until I finally learned my lesson.

• I started dating a girl who felt too perfect for me, so I ended things with her.
• Every time I broke up with someone, I ran back to my ex, using her to avoid loneliness.
• She's now engaged to someone else, and I've learned how awful and toxic I was to her.

There are many ways to describe that relationship we always run back to — the fallback option, the backburner relationship, or the Plan B.

As insulting as that sounds, I am guilty of using a woman as my backup option. Every time I ended a relationship, I would return to her, hoping this time would be different. Frankly, I used her as I waited for something better to come along. Nothing ever did because she was great, and I was the toxic one.

I knew the day would come when she would finally see me for who I really was — the guy who played games. That's why I wasn't too surprised when I recently learned she is now engaged, and she's had enough of me and my toxic traits.

As much as it hurts, I'm happy for her and glad I learned my lesson.

She was perfect, and I panicked

We'd been playing this game since 2011. I still remember our first kiss, to the sounds of a young Avicii playing "Levels." I was 19, and she was 17.

She was too sweet. She loved me too much. She was too available. Everything was too perfect, and that always left me wondering if something was wrong or missing. I had idealized love to an unrealistic and absurd level, so I found countless reasons not to pursue anything serious with her.

While dating her, I used my lawyer skills to walk the fine line of what was "allowed" so I wouldn't be liable for my actions. But there are no legalities when it comes to love and relationships. The truth is, I was spending time with her, creating a special kind of bond — one that, even to this day, would never be topped. But it was also a textbook example of a toxic relationship.

The real problems began when I left her and jumped into a relationship with someone else. But I still found a way to remain "friends," knowing she would wait for me. When I broke off my other relationship, I went back to her arms — just to jump into another relationship, leaving her behind again.

This happened four times. I never took her seriously. I was selfish and blinded by my idealization of love. But ultimately, the joke would be on me.

She's now engaged

Understandably, after every episode of our toxic love story, she grew further away from me. Each time I missed the chance to make things official, she slowly distanced herself from me. But the opposite happened to me: I grew closer to her and the idea of being with her — finally, and ideally, forever.

Life had other plans. She started dating someone else, and we stopped talking. After the last episode of my narcissistic game, she'd had enough and cut me off for good. Losing contact with her gave me the space I needed to reflect on my love life and the true meaning of loneliness. For the first time in my life, I felt alone. I didn't have my Plan B anymore. It was scary.

But it also helped me realize I wasn't OK with being alone. I realized I had convinced myself it was OK to use her.

I tried reaching out to test the waters, but she didn't want to talk. A couple of months later, I discovered her boyfriend had proposed. It wasn't easy. Even though I knew it was coming, I was devastated. Not because she was marrying another guy but because she seemed to be truly happy with him.

I've learned my lesson

I missed my chance with her. It breaks my heart to lose one of the best human beings I've ever met, but I guess that's the price I need to pay for playing games. All this time, I thought she wasn't good enough for me when, in reality, I didn't deserve her.

I've learned a valuable lesson that I've been implementing in all aspects of my life ever since: appreciate opportunities and don't miss chances. It's better to regret taking a chance than to wonder, "What if?"

Thanks to my ex, I now value prospects, possibilities, and opportunities.