How can I make my friend understand that her boyfriend is using her?
Sadly you can't, she either has to find out the hard way and find out for herself. Or maybe if you say something and give her some reasons she'll start to believe you but you can't force her too.
You can't make your friend understand. Sometimes this if people don't listen to you, then they gotta figure it out themselves... sometimes the hard way. :/
Well if other people notice it, try telling them to tell her so that way she can believe it more...
You can't. You can try to give a hint or two and be there for her when she does catch on.
Chances are you won't reach her until it is too late. You can try using specific examples against her as proof, but she will have to learn on her own. I'm sorry
just tell her. better now than later
How is he? Cause I might have an answer.