In the same situation
Hi, I came on here looking for something else, but when I saw your post I had to respond. Basically I am in the same situation as you. My mum has early onset dementia, and at 66 is in a specialist nursing home for dementia sufferers with challenging behaviour, she is now at the end stages of dementia and doesn't always know my dad. She doesn't know me when I visit, which isn't that frequent as I live in Yorkshire and they are in the Midlands and I have 2 young children that can't come to visit with me because of the behaviour of mum and other residents basically.
Anyway, my dad has been seeing someone else for about the last 3 years - I'm not sure exactly how long it has been but mum was still at home when the relationship began. I am finding it a complete and utter head scrambler. I am not religious so it isn't about the whole marriage vow thing, but it messes with my head. I don't think what he is doing is necessarily morally wrong, he is only 67 himself so needs and deserves to have a life. The person he married isn't there any more, except in body. He goes to visit mum on alternate days - which can be a trial as sometimes she is pleased to see him, other times she is aggressive and wants him to go away.
So, I have the quandary that I don't think what he is doing is wrong, but because mum is still there it feels wrong. I have met the lady - it was sort of forced on me, although I was willing to meet her, I was rather upset that I was given an hour's notice, and had to meet her when I had my kids (7 and 4) with me, as I wasn't sure how I would react emotionally. This was down to my dad rather than her though. She is very nice and seems very respectful of mum. She is currently living at my dad's house and has sold her flat, but she intends to buy somewhere else, and wants to ensure she has her own place - on that front I believe her. I've now seen her quite a few times, and it is nice to see my dad interacting with someone his own age on an adult-adult level. It was my dad who was the one who wanted me to meet her, as he wanted the relationship to be out in the open and for his friend to not feel ashamed, or worried about seeing people. I've been friendly and welcoming to her, and we seem to get along ok.
However, despite all that, it still messes with my head and feels wrong. I think the issue is that mum was very much a believer in marriage vows and fidelity, and so would be devastated by this if she was still with us mentally. I don't know. Just to say, you're not alone, I'm in this position too, perhaps a bit further down the line, and it is really really hard, but her presence has helped my dad immensely. As you can probably tell I'm all over the place with it though!