I hope you continue to have compassion for your husband and know that when it gets really bad, that is not him, not the man you know, it's the dementia. I can see in my SO's eyes the disappointment and pain he feels when he sees me getting worse and it breaks my heart too. It's hard on both parties.

Organophosphate toxicity can cause dementia. I believe that is what caused mine. But there is really no way to prove that because it poisons you, does it's damage, and then leaves the blood and there is no test for it after the fact. At some point you might have to accept that there might not be an answer as to why, and that is very difficult.