Delusional thinking.

Loved this response: “Continuing to meet them where, when and who they are at each moment is the truest form of love”.
copy and pasting for loved ones!

Jim, as difficult as it is you have to ignore her comments.
Do not react
Do not get upset when you are with her.
Reassure her that you love her.
Reassure her that you are there for her.
Hold her hand.
Paranoia and delusions are common with some forms of dementia and particularly LBD. (most common with Parkinson's)
Redirect when you can. But acknowledge what she said.
So if she starts like this...
"Jim I know you have a girlfriend and you don't love me anymore"
Your response could be...
" (Betty) you are the only one that I love, let's go get some ice cream" then go for a walk down the hall with her, holding her hand.

Just ignore her ranting. She has dementia so her brain doesn't work right anymore.
When she starts up about you having a girlfriend, tell her once or twice that it isn't true then totally ignore anymore mention of it. Do not address it again during the visit. She's in a dementia loop about and will keep repeating it over and over again. Many times ignoring it will eventually break that loop. It usually comes back, but ignoring the topic of it is the only thing that can work.

You've got a hard situation. If you have to cut back on how often you visit her and for how long, you should. Your mental health is important and you have to look after it. Good luck to you.

They really aren’t “accusations”.

Her comments are the products of her cognitive decline, and her inability to use facts to reason and reconcile inaccurate information.

Comments of this type are shocking, but really need not cause you pain. You are meeting her needs in the best ways you can, and you are not doing the thints she says.

Try “I love you as dearly as I did on our wedding day, and always will……did you hear about (whatever)” and see if you can deflect her comments a bit, but don’t expect her to change what she’s saying based on what you say.

Please don’t feel embarrassed if she begins to make these comments to others either. Anyone who works in an AL has heard them many times before, and anyone who gives this kind of comment any attention at all deserves to be ignored.

You are doing the best you can, so give yourself credit for that.

Sorry - I have nothing to offer but sympathy. My mother still blames me for making her grow old (when she recognizes that she is old) and is still grumbling that I married and had kids instead of devoting my life to her (or that I am about to get married).

It hurts to be on the receiving end no matter how incorrect.

We are dealing with this right now. My mother is convinced my dad and her sister are "going together" she is in a rehab facility due to a broken arm. She wants us to tell him to move in with her sister so she can go to her home and live in peace. They have been married 62 years. This has gotten so out of control she has tried to attack him and says she will stab him with a knife. Obviously she cannot go home at this point. It is so upsetting. I feel bad for you :( i agree with the re-directing and moving on to another topic. I do that but she always circles back to the dillusion.

From Verywell Health:

Why False Accusations Might Occur in Dementia
In dementia, delusions and paranoia can develop, causing the person to distort reality. So, rather than simply forgetting a loved one's name because of memory loss, dementia can cause the person to believe untrue things, such as the unfaithfulness of a spouse or partner. Paranoia can cause such distrust and fear that no matter what you do, you may be unable to convince your loved one with dementia that you really do love them.

How to Respond
How do you cope with this when you're doing the best you possibly can to love and care for this person? It's not easy, and there are no easy tips to make this disappear, but here are a few things to try. And, in trying them, remember that your goal is not to "win the argument" and prove something; rather, it's to comfort and care for your loved one.

Provide reassurance: This can occasionally work, and it's worth a try. Remind her of how much you love her and are committed to her. Be aware, however, that the person's delusion may be so fixed that you could reassure her repeatedly and get nowhere.

Take a time out: Remind yourself that the disease—not your loved one—is responsible for these thoughts and behaviors. Delusions, though clearly not accurate to everyone else, feel extremely realistic to the one who is experiencing them. Do your best to not take it personally by understanding that dementia warps the reality for your loved one. It can make it a little easier to cope if you understand that those hurtful words are coming from the disease, rather than your loved one.

Reminisce: You can try to direct the conversation to a special shared memory, such as when you proposed and she accepted, the birth of a child or a special trip you took together.

Distract: If you aren't able to reassure or reminisce, try distracting her. You can bring a favorite snack over to her or turn the television on to her show that she enjoys.

Validation: In general, I wouldn't encourage lengthy conversations about the accusation, but in some situations, it could be helpful to ask questions about what she feels you did. Perhaps she's fearful of a particular situation or person. Let her speak about her fears and work on not becoming defensive in response. This may be difficult emotionally but could help her process her fears.

Call reinforcements: Occasionally, some people respond well to one particular person in the family. For example, Is there one son who will be listened to and believed when others are not? If that's the case and your loved one is distressed because she continues to believe that you are being unfaithful, try having that son reassure your spouse or partner that you love her and will continue to be there for her.

Sense of humor: Sometimes, no matter what you try, it just doesn't help. The delusions and fear are so strong that you can't reassure her. You could try to use humor in this situation, perhaps by being self-deprecating. Try pointing out a funny fault of yours and say how glad you are that she puts up with you because you know that no one else could. As with the other possibilities, this may or may not be effective, but it has the potential to diffuse the anger, fear and hurt that she (and you) may feel at the moment.

Ask the physician: If this is an occasional accusation, do your best to roll with it. But if you're seeing persistent paranoia or distressing delusions, ask the doctor if medication is appropriate. Antipsychotic medications do have the potential for significant side effects, but they also can be helpful in relieving paranoia and delusions.

A Word From Verywell
Remember that in order to be an effective caregiver, you will need to seek support and encouragement for yourself at times. Don't hesitate to contact a local or online dementia support group, seek individual counseling or ask a good friend or family member who has a listening ear to meet you for coffee once a month.

Maybe redirect her by asking about the good old days?

Spend as little time defending yourself as possible. She can't understand, she will never understand, and it's best not to keep talking about it.

I'm very sorry. Have a variety of things to distract her with. Can you do magic tricks? Recite poetry? Ask her to sing songs with you? Seems crazy, but anything to occupy her very active mind!

You can always limit your visiting time and stop going as often. I'm sure you could use a break from the constant accusations, so recuse yourself for a while. Good luck.

Is she on any meds for anxiety/agitation? If not, it may be time. She can't bring herself around to a mental state of understanding or peace so it is merciful to provide the help for her to achieve a calmer state.

Delusions and paranoia are a feature of dementia, unfortunately.

When you visit her, try meeting at an event or activity in the facility so that she is distracted, then leave before the activity ends (ask a staff member to take her back to her room). Other than that, you will need to keep distracting and redirecting the conversation: if you have a smartphone or tablet, have it loaded with pictures of family members or pets, things that are still in her long-term memory, or turn on her tv to a pleasant show (animal, fix-it, biography, etc). You won't be able to "convince" her of anything since she can no longer use her reason and logic and memory. Even if you have to just walk out while she's lobbing accusations at her... it is what it is and try not to feel bad if you have to resort to this: you've done nothing wrong. May you receive peace in your heart on this journey with her.

Try humor. Smile at her and tell her that no 100 women could ever measure up to her. Tell her that when you see another woman you can only wonder at all the ways she can't measure up to the gal you have. If humor doesn't work try something else. But know in your own heart that this is the illness speaking, not really your wife. And know that this, along with thinking someone is stealing our stuff, is the most common thing our beset minds come to. We are a strangely acquisitive animal. Our stuff. For most animals it is "my shelter. my food. my territory". It's all that for us, but it's also "my family. my stuff". All inhibitions down we look to see who wants our stuff. Our money. Our hubby. And ALL our stuff!

Best to you. I hope she will give us this habitual circular thinking, but she may not. Try to distract her. Bring photos, help her paste them in a pretty album. Talk about memories.