My first post, no one to talk to

I am writing because I literally have no one, no best friend or family member who I can ask for support or understanding. I feel afraid. I've been married to my sweetheart for 51 years. Over the last 2 years she has been displaying memory loss. My son has noticed and others have noticed. At first, when either myself or my son mentioned our concern to her or asked her to get a medical evaluation, she refused to acknowledge the situation and still does. She becomes very hostile to me when I plead with her to get a check up, so at this point I have given up on that request. She is constantly accusing me of betraying her by discussing with our son, but he has noticed on his own. Her memory is to the point that my son doesn't want to have her drive our granddaughter to school or pick her up. Even with driving directions on her phone, she is constantly rechecking the device . But I think she is aware of it because she took up memory exercises such as jigsaw puzzles and crosswords. I believe she is terrified, because she had an aunt with dementia. My mom had it and I know what is coming. In my mom's case, my sister and family moved in with her to care for her, bathing and diapers included. I have always been my wife's protector to an extreme, and I have determined to myself that I will outlive her, just so I can take care of her personally all the way. We are going on 74 years old. The situation has deteriorated to where is is changing her personality and day to day behavior. She is becoming mean to me at times with sudden mood swings and sometimes saying very hurtful things. She gets confused on when she last fed a pet and when I try to remind her, she goes into attack mode. We are one of those couples that has been inseparable for our entire marriage, but honestly I hate to say it, I now frequently think she doesn't love me anymore. No matter what, I will stick it out but I am beginning to wonder how I will have the strength mentally. I am scared because she keeps talking about dying and afterlife, even though we are both very physically active and fit. She truthfully can pass for someone in her 50's, has always taken good care of herself. so, not sure where I'm going with this, but if anyone can offer helpful hints, I'm all ears. I am alone. I am uncertain. I am so afraid. And I love my wife, even though it's been really strained lately.