Hi @cat2023, my situation is so different from yours. My husband accepted his diagnosis of Alzheimer's Disease gracefully and was relieved to let go of tasks that were increasingly difficult for him. It's been a few years now and he generally functions pretty well. He has no short term memory and fantastical perceptions sometimes.
Your boyfriend is in a unique position as he is the person in charge of his business. If he were an employee, his dysfunction at work would be brought to management's attention and addressed through a disciplinary process and performance improvement plan or reasonable accommodation under the Americans with Disabilities Act, if he willingly shared his diagnosis.
I found this series of articles from Alzheimer's Society UK about denial of dementia and lack of insight. You can start with the first article and continue to the others by clicking on the arrow at the end of the article.
https://www.alzheimers.org.uk/get-support/help-dementia-care/understanding-denial-lack-of-insight
Also Teepa Snow is a great resource. You can Google her name and find articles or YouTube videos.
I wish you the best. Your boyfriend is fortunate to have you in his corner.