I appologize if I was too harsh, but she needs to first address her current marriage before even considering persuing this other guy. I think its completely selfish to stay with your husband just because your not sure if your love affair would continue if you split up.
Also this guy has told her that he is working it out with his current girlfriend so why try to sabotage that? This woman seems to be attracted to him because he is not attainable to her. He obviously feels bad that she feels so strongly about him and does not want to tell her that he does not love her, but hey maybe Im wrong. I just hate to hear people that consider only their own feelings and do not think how this could affect the others involved.
But I should not have said I hope you grow old alone, because even you deserve to be happy. Just try not to affect other peoples persuit of happiness in the journey to find your own!