Hello and Thank You for using Just Answer. The more you forbid your daughter to see her "boyfriend", the more she will sneak around and be drawn to him and continue to be sexually active.
If you can persuade her to stop seeing the gentleman and she truly agrees, then power to all of you.
However, if she attends the same school as the gentleman and wants to keep seeing him, there is not much you can do but maybe try to change her to a different school. If that is not possible and you talk to her about having sex at an early age and the possible consequences (pregnancies, STDs) then that is about all you can do. At age 18 which is only 2 years away, she will be legally an adult.
Nowadays, children grow up too fast. The media influences them especially on MTV with a show called "16 and Pregnant". Girls are trying left and right to get pregnant to try to be cast on that show. It is a shame but that is what our society has come down to.
Just try to instill all the positive moral values that you can to keep your daughter on the right track.
Have a great evening!!!