I know what you are going through. My daughter is now 23 but when she was 18 she began dating someone who I did not think was right for her. He wasn't older but I just knew he was not the right one. At first I let her know how much I did not like him but eventually I realized that the more I spoke against him, the more she was determined to be with him. She actually dated him for about 3 years but I think if I had just gone with the flow instead of letting her know how I really felt, she would have broken up with him sooner. My advice to you is to ride out the storm. If forced to choose at this point, she will probably choose him just because kids that age don't want to admit mom is right. She'll probably drop him sooner if she thinks she is doing it because it was her idea & not moms. Oh, by the way, when my daughter finally told me they had broken up, I just said, "Oh ok" & that was it. I didn't make a big deal about it. Hope everything works out with you.