MIL and her priorities!

Absolutely no need for name calling. Keep it civil

is also textbook behavior. people who have been in very long marriages and are elderly tend to re-partner very, almost shockingly quickly.
Where did this 'fact' come from @Ponderingwindow ? Because in the UK, this is hardly borne out in reality
And 're-partner'??? That is an abdominal non-sensical mangling of the English language

Cross post but how is it possible to have not accidentally run into her if you live in the same village?

What am I reading?
Your 60 year old MIL sho was very supportive with your DHs children from his first marriage, worked full time while also caring for her husband with Alzhiemers and nursed him for 18 months at home is now living her life and your DH is acting like a petulant child.
He needs to grow the f up.

I lost my beloved Dad last year in his 60s (not to dementia). My DM is utterly bereft still18 months on. She turned 70 last week. If she could find a glimmer of happiness in her world of pain I would be happy for her. I think your DH needs to try and be happy for her instead of carrying bitterness, she is only 60!

I have three adult DC. If any of them thought I needed their forgiveness after nursing their DF through dementia and seeking comfort (it sounds like you don't live close by), I'd tell them to stick it. How dare he?

I agree. People who have a partner with senile dementia of any type feel as though they lost them a long time ago. As long as they care for them as much as they can, don't shirk responsibilties towards their ailing spouse, one cannot blame them for finding some joy elsewhere.

In your mother-in-law's case, op, she has now found someone who really understands because he has a wife with dementia. He and mother-in-law give each other comfort.

We cannot judge. She sounds like she is basically a good person. We don't know what we would want, or do, in her position. You haven't said how old she is, she may have a lot of life left in her and much love to give.

I’m honestly shocked at how selfish you and your husband are coming across in this post. Why on earth shouldn’t your MIL be in a relationship? You seriously believe she should sacrifice her own happiness to be at your beck and call and giving your baby 100% of her attention?! She’s just had the trauma of losing her husband to dementia - and having a relative with dementia myself, I’d argue he was lost long before he died - and is trying at another shot at love and you are begrudging her this? Seriously? Give your head a wobble. Surely nobody is this self centered.

Wtf?! 'Loose'??

You and dh need to stop thinking mil should be on a pedestal.

She's human, the affair isn't great but it's none of your business. I wouldn't begrudge her some relief from having a husband dying in a care home.

She's had a rough time that neither of you have experienced so you don't know what it's like. I'd cut her some slack and stop making it us or him.

It sounds a lot like MIL has spent a very long time putting everyone else first and never herself.

Good for her.

All was ok as it could be, MIL making effort with youngest, for 6 weeks.
She then starts seeing someone else, DH hits the roof. MIL ‘puts family first’ and the relationship becomes a friendship, except of course it’s now a relationship behind closed doors.

Your DH sounds controlling - what right does he have to 'hit the roof' and make his mother hide her relationship?

Another one on MIL’s side here. Women do the primary care for children elderly relatives and often their spouses throughout their lives. The last 2years were probably an utter grind for her. She’s in her 60’s and she is probably trying to find some happiness now. The thing about watching anyone decline and die is it really brings home your own mortality to you. You know you only have so much time on this earth.

I would also say that if she loved FIL she’s been losing him piece by piece for a while, I can’t imagine the grief I would feel to watch my DH go through that. If it wasn’t a happy marriage then she gets a second chance.

Your MIL has a bratty son problem. Her son needs to grow up, realise how shit that dementia is, that his mother is allowed to have any relationship she likes and that he is not the centre of the universe.

Honestly he's behaving like a toddler demanding she put him first. What about her? She doesn't owe your child anything. It's not her responsibility.

Is your husband like this with you too? Wanting you to make him the centre of the universe?

This is desperately unhealthy and has red flags.

Your DH should get some counseling to explore his feelings iof grief and resentment. I feel sorry for his mum to be so judged by her Ds. Would he be happier if she was lonely ?

I think your DH may have to try to separate out his grief for his father and his current feelings about his mother. He's projecting his anger at the loss of his father onto his mother's behaviour.

He can't presume to know what went on in their marriage before his father was obviously ill, and died. Your DH has no right to demand that his mother behaves as he thinks she should behave. She may have done her grieving already.

It's tough, I know - parents' behaviour always has an impact on their children, however old they all are. But your DH is not a child, he is an adult, he needs to deal with this in a more adult way - you said he "hit the roof" - why? I wonder if it's because he couldn't escape from having to acknowledge his mother is more than a mother, but an adult woman with desires etc etc. independent of him, and of your DH's father.

I had a friend years ago who started an new relationship the month of the death of her DH, if not earlier. Terminal illness and death do strange things to people living with it.