I must admit she seems happy with him, and she says she loves him. But she has many friends and activities near where she lives, and doesn't need to get married. Sorry, but we don't think that's possible. Unless your mother's intended husband has serious health problems that threaten to turn your mother into a live-in nurse immediately, or unless you have evidence that he has designs on your mother's money, we suggest you grin and bear it. Although your mother has been living alone for years, she may crave the companionship that a marriage brings.
Many people feel more comfortable in a committed relationship.
By all means, encourage your mother to request a prenuptial agreement that keeps her assets from passing to her husband and his family. But it might also be constructive for you to consider why you feel uncomfortable with a new relationship that is clearly making your mother happy. My father died early this year, and the family hasn't been the same ever since. It's not just that we miss him, but we can't seem to get along any more. My brother seems to think that his opinion is the law of the land.