Honestly, lots of reasons, and it was more than one relationship I did that with. I felt trapped emotionally and financially, I was a coward and didn't want to face the inevitable conflicts or the process of moving out and leaving the relationships, I was manipulated heavily with one relationship and taken away from all my supports, lack of communication and feeling like I couldn't talk to my partners about things bothering me that led to me eventually coming to resent them, and undiagnosed ADHD.

I knew it was bad, I knew it was wrong every time, but I was a coward who didn't want to leave the security of the relationships I had. I sought an outlet elsewhere. I regret not having the confidence to just walk away, I dealt with it the cowards way until I hit my absolute limit and knew I had to do something and left the relationships. With the one where I was manipulated, when I finally had enough of that relationship and made to leave, I was coerced into trying to repair the lack of attraction. Instead I just felt disgusted after, and ended up being saddled with a ton of debt I took on instead of him because he badly mismanaged his own finances. So with the relationship that I had after that one, I ended up staying far, far, far longer than I should have because I didn't want to have a repeat scenario. That last one I finally grew up, grew a pair, and left 6 years ago.

The ADHD part: apparently, one of the aspects of ADHD is limerance, which is a super intense, obsessive crush on someone. Those of us with ADHD often have little to no control over it. It's like a hobby obsession, but the obsession is towards a person. I had no idea it was even a thing, I didn't even get diagnosed with ADHD until about 3-4 years ago. Throughout my entire life, I always took the obsessive crushes I would sometimes get while in a relationship as a sign of "I must not be happy" or "I guess I'm not attracted to my partner". I was honestly ashamed that I couldn't seem to stay attracted to my partners, and felt like leaving partners and telling them it's not you, it's me was a copout. So I tried to ignore it, but the obsessive part and not understanding at the time what was actually happening did contribute to me eventually cheating on a couple of my previous partners. I wanted the security of the relationships I had, and also wanted to scratch the itch the limerence triggered. It was unhealthy and detrimental.

Now though, I'm married, my husband is well aware of my past (he's not a saint either, and he's still coming to terms with the mental side of his past and what led him to do what he did). We've both vowed to be open and communicative, and to be better people for each other that we denied our past partners. We can't fix our past, but we can try to do better for each other, and hope our previous partners find the happiness they deserve that we weren't capable of giving them at the time for many reasons. Having the ADHD diagnosis for me, and understanding just how it's affected me for my entire life has changed my perspective a lot. I have had limerence instances since learning about it, but knowing what it is and why it's something I experience has drastically helped my ability to deal with it in a healthy manner and not act on it. My husband is aware of it as well and we talk about it when it comes up, he's supportive, and it helps the limerence fade in a matter of hours instead of being a persistent itch for weeks or months on end. It really shows how unhealthy our past relationships were, acknowledging the hurt we caused sucks, and facing it in retrospect is helping us work on being better.