Is it possible to get memory care for someone who is in the very beginning stages of having a problem?

My grandpa lost my grandma last year, and their children (my dad and uncle) have been gone for years. I have taken charge of being there for grandpa in whatever way(s) I need to be. He cannot read or write, so this has meant paying bills and helping with medicine and taxes and doctors appointment so far. Not too bad, he lives five minutes away thankfully, and still drives at 80 years old. He's in "decent" shape physically. I am seeing a definite mental decline though. First of all, he has become convinced that my grandma's angel is living with him. But he doesn't think he's seeing an angel- he thinks she's really there and there was some scientific experiment done to bring her back. He sees and feels her at all times. He will say things like "I have to get home, she'll wonder where I am". His doctor is aware and believes it's an extreme grief response. But now there are more warning signs. For example, he forgot that I invited him over for Christmas dinner, he called me to ask about something else and he actually argued with me that it was Friday and not Sunday, and that Christmas was on Tuesday anyway. Also... he is starting to do some seriously reckless things. We had a big snowstorm and he went and out and drove the next morning in -20 degree windchill and totally iced over roads. And then called me to come rescue him! I have an eleven month old at home who couldn't go out in that. His car ended up getting towed and now I'll have to call around and find it. I don't know guys, you've always been very helpful when I've had questions before. My biggest question is: so, when he's clear headed, he's still very much so. He's clear headed more often that he's seeming off. How can I go about getting him care if that's the case? He is 100% against home care, he won't hear of it. He won't allow anyone to help but me and my husband.