Can our daughter, who is almost 18 and having sexual relations with a 15 year old, be charged with anything?

We recently found out that they have been haing sex for about 5 months. They have been sneaking in the back door of our house when no else is home. We warned her that she could be putting her entire future in jepordy. The boy has violent tendencies which came to a head this week. He kicked in the front and rear driver's side fenders on her father's truck. When we went to file a police report, the boy's father threatened to file charges against her. In the past when she tryed to break up with him, he harrassed her at school and called her all hours of the night and continually drove by our house. We have tryed to not let them spend any time alone but the boy's father doesn't do anything about it. Is there anything we can do and is she messing up her future? - Is this your question? Add additional information