Oh my yes, show her the messages if you can. She'll be furious with YOU, but she'll probably buttonhole those people and demand an explanation, and then she'll get to hear that her boyfriend is trouble from someone who knows him and ISN'T HER MOM. Perhaps that will help. (My girl turns 19 in a week or so, and I still have to use her friends as sockpuppets since Lord knows she won't listen to her parents )

I'm sorry that she's making some poor choices, but take heart if you can from the idea that it sounds like she doesn't cut often or lie often (or you'd be more resigned to it by now), yes? And at 18 she'll have opportunities she didn't have before...we all dread that as parents, but we can seize it and use it to our advantage as well. College or community college or job in another town, places she can go to meet NEW people instead of him...it's a lot of work, I know, but there's an opportunity coming your way soon