Well I hope they stay together because he makes her happy. You need to stop being a meddling cow or she'll start to cut you out of her life. He's a person, not a 'thing'.
Simply put you cant. There is no way you can convince her she's not in love with him because you don't know that she isn't. The first thing you need to do is to take a step back and have a long hard think about why you feel this way, is it really an issue with the boyfriend or do you have some unresolved issues from your past?
Either way this sounds to be your problem and I suggest figuring out why before you speak to your daughter otherwise damage will be caused. Then comes speaking to your daughter, you need to be honest with her but sensitive to her feelings, she is in love with this boy, you coming along and giving her a bunch of reasons why you shouldn't be with him is never going to achieve anything. Explain your feelings, explain your concerns but don't tell what you say she needs to do!
You are never going to get what you want, but if you handle this right you could walk away with your feelings heard and perhaps even respect from your daughter. The last thing I think you should think about is your parenting, do you think you have been a good parent? Do you think you have tried your very best?
Do you think you have brought up your daughter well? If you answer yes to all these then you shouldn't need to worry about her decisions, you should trust your parenting enough to know she will do the right thing for herself, yes she will make mistakes, as we all do but overall she should be able to stay clear f anything damaging. If you don't trust her to do this then what does that say about your parenting?
And in fact if you haven't brought her up as good as you should have then what gives you the right now to tell her how to live her life? A lot to think about there. Hope I have helped :) Hope I've helped.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.