I'm just coming out of a relationship with the same feeling. I made the mistake of marrying and having a child with this guy though. Considering that they don't live together, it will be much easier for her to break off. Once you get to this point, I've noticed it's nearly impossible to ever go back. I tried making things work when I wasn't happy for 4 years. I wasted so much time when I could have been happy. I hope for your friend's sake she can find the strength to end things before it gets any further.