Hello and Thank You for using Just Answer. Your daughter and boyfriend were actually laying down??? It is your house and you establish the rules that you feel most comfortable with. You must let your daughter know your rules of the house. Oddly, some parents allow their teen age children to have sex in the house and actually know about it.. Fortunately, you do not seem to be THAT kind of parent. Nowadays, children must have boundaries established. Just have an open and honest conversation with your daughter explaining that you do not mind if her boyfriend comes over or other friends. However, when a member of the opposite sex is over, the door must be left wide open and you would prefer there be nothing more done that hand holding and possibly kissing in our house. Also, you must establish an evening hour where she is not allowed to have her boyfriend over past that time. She will probably engage in heavy petting still, though outside of your house. If you have not had the "sex talk" with her, you need to or even refresh her memory. An 18 year old boy, who is legally an adult, usually has one thing in mind: to have sex with a girl...no matter how nice he may be. So please tell your daughter all of your feelings in a caring manner because whatever you tell her "not" to do, she will find a way to do it.
Hope this provides some insight. Thank you and have a nice day.