My husband and I found out that my 19 year old daughter has been having .?

She doesn't think that this is a problem. She has know the boy since she was 14 and had been steadily dating him for more than a year now. Because of this and the fact that she is on birth control plus they used a condom and he pulled out, she doesn't see the problem. We prohibited her from talking to or seeing him for three weeks in attempts to separate them, but she remains persistent on seeing him. We allow them to talk over the phone now, but they are still not allowed to see each other. She has been completely miserable, but my husband and I would just worry too much that they will have again if we allow them to see each other again. In the fall, the two of them will be going to the same college and we do not know how to handle this. We have considered making her switch schools, but that seems a little extreme. What should we do?