DEAR ABBY: My niece, “Amanda,” is 19 and fairly close with my daughter “Hayley,” who is 18. Since graduating from high school and through her first year away at college, Amanda has been going out of town to meet men she meets online. Amanda shares her location with Hayley through Snapchat “in case something happens.” My niece is doing this without letting anyone (other than Hayley) know and often uses my daughter as a cover to her parents. These aren’t just dinner dates, but usually weekends away from home. Hayley always tells me when Amanda is away. We are both concerned about her behavior, a…