Asked by my Grandma

I'm 26 and doing well career wise and okay relationship wise, no steady girlfriend at the moment. Last month I was over my grandma's cottage doing some minor repairs. Anyway, I was asked the usual questions. You know got a girlfriend yet and if not why, but then there was another question. Would I do her a great big favor, without asking what I said I'll do anything for you. It's a strange request she said, but added I need someone to fuck my widowed 62 friend as she is getting dementia and I've read that regular sex can help prevent it. I've met her friend many times and she was quite good looking for her age and 5 years younger than my grandma. I asked why me and was told I'm the only one who is unattached she knows, who was still capable of fucking. I don't think she would want me to fuck her I replied. Yes, she would as I've discussed it with her after I read about it, she replied. Not sure what to do and my grandma could tell I was unsure of how to respond, and she said why not try it once and if you can't go thru with it, it will be okay and if you can well go for it. Arrangement was made for the next Sunday after their attending church. I turned up and grandma and her friend were waiting for me, probably expecting me to back out. Anyway, her friend looked great all dressed up in her church clothes. I decided to see if I could go thru with it, so get getting up they both gave me a massage. I was totally naked and once they had done my back, I was told to roll over and my grandma had left the room and her was totally naked now also. She continued by massaging of my front, and I got a hard-on. So, she mounted me, and I gave her a fucking and we fucked twice that day. I've been fucking her regularly now for 3 months, I'm really enjoying the sex. Whether or not it's helping with her dementia, I don't know or it's too early to tell. I'm quite willing to keep fucking her as long as she wants. Maybe my grandma might need some dementia prevention as well, I think she is a really horny woman.