explaining struggles to partner

for context, i am diagnosed with lvl 1 autism, was diagnosed asperger's as a child but obviously diagnosis has changed. i am a heavy masker as i work retail, so my only time unmasked is at home with my boyfriend.

we've been together almost 3 years, we've lived together for about 2. he is very supportive and always is happy to help me when i'm overwhelmed. he helps me when i struggle with food, cleaning, etc. but i feel like he doesn't actually understand why i Can't do those things sometimes. i don't know what words to use to explain how disabling executive functioning issues can be. i'm not lazy, in fact i'm laying there mentally tortured over not being able to do those tasks; but I literally just can't do it. i'm having a hard time getting him to understand this feeling without him just thinking i'm lazy or "childish". it's starting to make me have doubts in our relationship, which is terrifying as we are trying to buy a home and talking about getting married.