I actually think your situation doesn't look as bad to an employer as you see it to be. 2.5 years at a company is pretty standard for this day in age and it doesn't seem as if you lack commitment. You also had a long commute, which is a reasonable reason to look elsewhere.
On your resume, I would keep out any reasons for leaving or any of your mental health information. That information isn't their business and it's not the place to do it. Save this one for the interview but only if they bring it up. If they have an issue with a break in employment, or any other issues with your resume, that's the time they'll ask. I would suggest that your response be as positive as possible.
I would practice a response saying something positive about the work but then saying, "but that work-life balance wasn't sustainable to me due to the commute and due to wanting something different from my career and knowing I had to take the next step towards something else. I realized taking a break and reassessing my situation was the best move for me and during that time I (insert something you learned or realized while you weren't working)
If you have any concerns about focus at the job now, you will be filling out an EEOC employment form that asks you if you have any disabilities. I believe ADHD is considered a disability that you can indicate there.