can you make a guy love you for having sex with him?

I have a friend who loves this guy so much and still loving him in spite of the fact that the guy is loving another woman. They're officemates and childhood bestfriends. For years, my friend have shown him her love. She would be attentive to his needs, always there when he needs her and gives her shoulder to cry on. But the guy has considered them a plain friendly sympathy and no malice at all. My friend will say, "He's too naive" and I do agree. His friend is now having a conflict with his girlfriend and they're always together talking about her. My friend finally said, "What if I make love with him? Will that make everything clear?" I don't know if that's the kind of sign he's waiting but my friend is desperately in love and she wants to break the rule.
All of us, has someone we want to be with our lives but what if that person is just ignoring us? Do you think, having sex is the ultimate option to get him or her and eventually to make him or her fall for you?