mojo is "on the mark." Your father already has a "relationship" and I notice that you are not concerned about that, but you are concerned that your mother has found a relationship that makes her feel some happiness, more youthful, and giddy. Personally, I think your mom has invested enough of her life into the drunk, needs to divorce (if she can financially afford to do so), and get on with her life. Her years are getting fewer and she should not be encouraged to waste any more of them.