My manipulative 86 year old mother wants to marry a 68 year old man.

This is the third time my mother has lived with me, and I’m her only child. She has always been hostile toward my ex-husband and is still unkind to my current one.
The first time she stayed with me was after my father passed. She resented the monthly mother–daughter dinners I had with my adult daughter, kept money my dad left for us, and then told people we were trying to take her money when we confronted her. I suggested a retirement community, and she twisted it into me “trying to put her in a nursing home.” She secretly found a condo, moved out while we were at work, and disappeared for three months. That was 2013.
In 2020, she thought she was having a stroke. I had moved to another state by then. She wasn’t stroking, but she began losing sight in one eye, and with COVID spreading, I told her she could stay in the in-law suite in our new home. She moved in and immediately began complaining and disrespecting my husband.
In June 2021, while my daughter was recovering from surgery at my house (and waiting on cancer results), my mother told her she planned to move out while I was away. She said nothing to me. When I told her I knew and that her brother wasn’t allowed on my property because of past behavior, she called Adult Protective Services claiming I threatened to shoot them—even though I have never owned a gun. A sheriff, APS, and a moving truck showed up. She even led them to believe the house was hers until I proved otherwise. Once they realized what was happening, the sheriff actually empathized; he’d experienced something similar. She left and went no-contact for months, never even checking on my daughter—who thankfully did not have cancer.
Fast-forward to 2023. After a heart attack, it became clear her brother was burned out. My husband said she should stay with us, but I refused; I knew what would happen. We found her an independent-living community after she recovered, but she didn’t like it, so we moved her to another one. She complained there, too, and after a fall, she moved back in with us—and the same patterns resurfaced: coldness, judgment, refusing to acknowledge my husband, claiming she “didn’t hear him,” and telling him this was my house, not his. It hurt him deeply.
Meanwhile, she’s been on-again/off-again with a “preacher” since my dad died. Recently he mailed me $30 and a letter asking me to buy her roses because “he couldn’t find a flower shop that delivered” (not true—he just has no credit card). Then he called to say that my 86-year-old mother “just does it for him.” He lives in an unsafe area, nothing like where my mom has ever lived. Now she’s sneaking calls and likely plotting how to move back with him. He is 68 - young enough to be her son as I am 60.
Her doctor says she has cognitive decline. But beyond that, my mother has always had narcissistic traits—lying, hiding things, twisting stories, and doing whatever she needs to appear superior.
I am exhausted. Everyone has warned her the man is a scammer, and she refuses to listen. I’m now preparing to get medical and legal Powers of Attorney to protect her, but emotionally, I’m at my limit. Yesterday she stayed in the car while we ran into Walmart to grab three things. We came back and she didn’t see IMCU’s. When I opened the door. She was on the phone with that man and hurriedly trying to end the call but he kept talking. I am tired of her antics, disrespect, lies and manipulative behavior. There are days that I want to either take her to a nursing home or a mental facility and check her in. We can’t travel without her and when we take her she ruins the trip. We took her to our hometown and she stayed with her cousin but I later learned she went to stay with that man. She could end up with an STD or worse! She is behaving like a pre-teen in diapers! She has always put on a front for everyone but we know who she really is and we are all exasperated. Any suggestions?