This type of behavior, failure to recognize a second spouse, is not uncommon where mid-to-late stage memory loss is involved. It’s a complex issue, and not knowing the complete diagnosis
and the extent of your mother’s vascular deficit versus the level of Alzheimer’s memory loss, it is difficult to provide a precise response. However, having said that, there are a number of points I can make that may help you understand the situation and there are some things I’d suggest you consider doing to mitigate the situation.
First, I believe that you did a very good thing by putting the wedding photos around the house, but they are apparently losing their effectiveness. Keep the photos around and continue reminding your mother about her current husband, but don’t expect to see an outcome different from what you’re currently experiencing.
To your mother, her husband, “that man” may be a total stranger because she is not rational, and her mind and memories are living and recalling events from a distant time frame – perhaps between 1950 and 1985, which did not include her current husband.
I suggest that your mother have an updated neurological exam to determine which form of dementia may be the culprit in causing this increasing lack of recognition problem. It’s possible that in your mother’s situation, the Alzheimer’s disease may be entering a stage where she is mentally living at a time in her distant past. That would help explain why she does not recognize her current husband, even though they’ve been together for almost two decades.
A neurological evaluation may lead to a prescription medication that reduces your mother’s anxiety and improves her reaction to her husband, although she may not accept him in that role. Be aware that some patients can escalate emotional behavior to levels of severe agitation and even become quite combative, thereby becoming a danger to those around them as well as to themselves.
If your mother continues to fail to recognize her current husband regardless of a new medication, he, you, and the rest of the family may have to agree that to appease her, based upon her level of debilitation, her husband may have to “become a family friend” or be introduced to her as another “relative of the family.” He may be a friend or relative that is there to help out, which may be a way to get her to lower her defensiveness. It’s a terrible situation in which to place her husband, but it may be the only way that she will accept a “stranger” in her own home.
Also, dependent upon the results of her neurological evaluation, her level of debilitation, her need for assistance with activities of daily living, and the level of agitation, aggressive behavior and combativeness, it is possible that you and her husband may have to consider other options. For instance, can the family afford to bring in outside assistance such as a home health aid to do what her husband is no longer permitted to do, like bathing or dressing his wife? Can your mother safely remain in her own home or might she be better suited to a skilled facility that specializes in caring for advanced cases of memory loss?
These are just possibilities, and with no more information about her overall mental status than what was provided in your question, my response only points out these various approaches to a solution. I am not suggesting that your mother needs to be in a facility. But the big picture, both now and as her disease progresses will require you to ask and answer difficult questions. Those answers under the best of circumstance will provide you with a course of action that will be best for your mother, her husband and the rest of the family.