How can well-meaning relatives help a loved one proceed with caution when getting into a new relationship, after the death of a spouse?

It was less than six months after my uncle died, when my 85-year-old aunt invited a younger man to move into her house with her. She didn't ask anyone's opinion; she just did it. We were stunned, but she didn't give us the opportunity to comment nor did she ask for any advice on the matter. She told us she didn't want to know the man's background. She seemed to think highly of him and was flattered that he was interested in her. After a couple of years together, my aunt told us she was giving her house to this man, and several years later, after she was diagnosed with dementia, this man married her. She was enthralled with him, but I remained skeptical, as he was quite the drinker and whenever I saw them together, he was pouring himself and her a drink.

Throughout the time my aunt and this man were together, I often thought I should contact Adult Protective Services, but I refrained, as I did not want my aunt to get angry with me. She seemed quite enamored with this man and was not seeking my help. However, as the years went by, this man's health began to fail and my aunt's dementia worsened. Eventually, he was in/out of the hospital and my aunt wasn't able to live alone safely in her home. Finally, well-meaning family was allowed to step in and assist my aunt in moving to a memory-care facility, so she could get the care she needed. During this time, the man passed away. Fortunately, because he died before she did, her money (if any remained) was reinstated in a trust that my uncle had established prior to his death. Potentially my aunt will be able to afford her long-term care living arrangements, but it was very questionable for a time, as this man was quite the con.

I'd like to forewarn others about this exploitative situation and find out if there is anything we could have done earlier to prevent it, or just how family/friends might help when confronted with such a sociapath like this man. Any thoughts or resource suggestions would be appreciated. Thanks!