My friend has relationship problems. How does she fix this?

My friend has been with a man for 12 years. She is 27, so she has been with him for most of her young adult life. Recently, he has been asking her to have a threesome with another man. She doesn't want this to happen. He gets angry with her when she says she doesn't want to do it. He tries to give her options to make it easier, like, "Well, would you prefer it to be a man or a woman? I can just get a woman to have sex with you and I can watch if it makes it easier." and other weird things like this. He never takes into consideration that she DOESN'T want to do it period. He says that he's getting bored with the sex and he wants to spice it up, but she feels like it's too much to try to have a 3rd person in. He wants to try rough sex and bed restraints and things like that. She just doesn't know how to handle all of this. After her saying many times that she doesn't want to do this, he is relentless and keeps asking her to. She is getting to her wits end. I've suggested that she gets some couples counseling, but I don't know if they'd go for it or not. Advice??