ADHD Partner (Me) Needs Help Managing Tone When Interested

Hey all. I will BOLD relevant info for the skim readers. Keen for help from non ADHD and ADHD participants. 

Currently reading "The Couple's guide to Thriving with ADHD" by Melissa Orlov & Nancie Kohlenberger

I am not married to my partner but I have severely been rubbing her the wrong way with this reoccurring issue. I am a 27 year old male and she is a 21 year old woman for reference. 

When I don't understand which parts of what I said weren't understood, I always want to know which bit was misunderstood so I can recall the needed bit before I forget it. Repeating every single part would be exhausting so I try and grab with a quick question the bit they need before the sentence flies out of my brain and is lost to my shitty memory. Typically of ADHD, I usually say too much even when I try not to. That lines me up to fail as it reduces the likelyhood I will recall things too. 

All that sounds pretty reasonable though that was just the setup, but anyway the issue is what I sound like when I am trying to get that rushed question of which part is not understood. It is flat and emotionless and it squashes her and makes her feel like I think she is stupid or annoying. We have talked about why it happens but what I am at now is just admitting I probably can't remember anything of what I just said, which if you are ADHD yourself makes your normally invisible deficiency feel painfully visible to admit you can't remember something you said 3 seconds ago and that makes you feel even more broken than usual

I feel like the intense sounding questions are me gripping onto my own brain to cope with poor memory, but all the mental intensity I use to control myself leaks out and makes her feel like garbage

Has anyone had any experience with this?

I need some advice. I don't mean to hurt her. I want to hear everything she says and I want everything I say to reach her and be understood by her. Do I have the wrong approach here? I feel like it isn't too late to make a relationship that works here and of course I would not want this to lead to her no longer wanting to cope with me.