Relationships can get very muddled as dementia progresses - and it is disconcerting to witness at times.
The first time my husband went into a secure unit he became close to a female patient. He didn't think they were married as such (he knew I was his wife but thought we might have divorced). The two of them had a noticeable closeness (purely childlike) and used to communicate in what seemed like a secret language mixed in with telepathy. They were happy in each other's company but the lady could become upset if I led him away anywhere when visiting.
Earlier this year my husband had to return to a secure unit. During his time there I saw a lovely lady who was convinced that another female patient was her niece and she wouldn't let her out of her sight and became quite upset if staff tried to gently separate them for any reason, whether it be sleep; medical care or an outing.
Eventually the 'niece' left the unit and the distraught lady latched on to my husband , insisting that he was her son. I can tell you that she made quite a formidable mother and mother-in-law! The staff were brilliant at keeping tensions down both when I was visiting and when I had left.
Easier said than done, I know, but try not to worry. Confused relationships are certainly something that staff at the care home will have come across before and they will have strategies to keep the situation under control.