Working through acceptance

I'm new here and finally got the courage to create an account and post.  I'm 33 and was diagnosed 3 years ago with ADHD-C.  I've been with my SO for 15 years now and this explained so many of our issues.  We have worked through a ton of our struggles but there is one struggle that I can't seem to get past.

Acceptance.  Acceptance of my limitations.  

For years we talked about the person I "could be"... and sometimes I can be her...I have days where I get everything done plus some, and live like a normal person... but I am having to accept there are days I cannot.  Some days I just can't do the things as fast or as good as we want.  Some days I just can't handle a conversation because it's just too much to pay attention and listen.  Lately we are planning a big change for our life and we are seeing all the little ways in which my ADHD holds us back (usually with delays in decision making) and I am feeling so much shame. So much guilt.  My SO is very supportive but of course is also having to accept that the person he thought I was (or could be) probably is not going to be who I am.  At least not 100% of the time. 

I just feel so alone and so lost in these moments, where I have tried my best and I am seeing just how it's not good enough.  How I am not meeting his expectations.  How I am letting him down.  It breaks my heart to see him frustrated and know that I simply cannot change it.

How do I deal with these emotions?  It's going to be something I deal with the rest of my life, and feeling depressed every single time I encounter a set back due to my ADHD is exhausting (emotionally and physically).  I don't know where to go from here, it feels like a cycle I'll repeat every time we want to move ahead in life, or make new changes, or do anything out of my comfort zone.  It is so hard to feel like an adequate partner when my SO has to do so much on his own in terms of decision making, research, etc. when wanting to improve our life.  

Any advice is greatly appreciated, or even just to hear from someone else that I am not alone in feeling this way.  Thanks to all who read and share :)