Recently diagnosed but still destroying relationships

Hi everyone,

I was diagnosed with ADHD a few weeks ago, but I'm yet to be treated. I'm 32.

My life has been filled with turbulent relationships, particularly romantic relationships. 

Early this year I met an incredible partner online and we subsequently met in person, even though we were in a long-distance relationship. I had already been seeking answers to my troubles in life for a few years and was on an ADHD diagnosis waiting list when we met. We quickly came to understand that we were both sufferers, which drew us close. I have had many short and sharp dates and relationships where the other person cannot handle my ADHD symptoms, most notably my seeming inattention. So I felt understood and that I could unmask myself a little more than with anyone else when I knew she had an understanding of my issues.

Prior to this, I had been speaking online with another woman who I was close with, but for many reasons (including regularly investigating my social media for interactions with any women, however innocuous) was hot and cold for over a year. We never met because I didn't feel comfortable meeting. Unfortunately, I did not cut these ties when I met the ADHD partner, for reasons I'm not totally clear on. Perhaps I desired positive reinforcement. 

My new partner that I have been so happy to be with found out that I had been speaking with this woman, as she contacted her after seeing my interactions on social media.

I'm totally devastated that I have hurt people with my actions and broken the trust of someone who I care deeply about, and have probably lost my relationship with her. I'm ashamed and angry at myself I feel that I don't have control over such simple things as ending the conversation with someone who I don't even wish to communicate with anymore. I wanted to commit to my new relationship but somehow still managed to damage it. 

I feel like maybe I'm just a bad person and using ADHD as an excuse.

I'm confused about myself and what causes me to sabotage myself like this?