Is my 19 year old daughter being rebellious. Why does she continue to see this 24 year old man after i forbid?

her in doing so? She was dating a 24 year old man for 3 months before she finally decided she was going to tell me and her father about it. Of course we automatically disapproved. So she told me she would stop seeing him. But a friend of mines is constantly seeing her and this 24 year old man getting 'hot and heavy' in the public eye. She said they were kissing passionately outside the library of a school. Now we have always instilled good moral values in our children ,i dont know where we went wrong with this one? I told her as long as she is still living under MY roof she must follow the rules and regulations that i have designed. and she shrugged and said " okay i will". We are paying for her food and shelter the least she can do is obey