Please don't be judgemental..

I was talking with my sister the other day and she said that even though she is in a relationship with her boyfriend see is seeking for sexual attention from a woman. Her boyfriend is always working and never home. So she is lacking that sexual attention. She really doesn't want to cheat with a man but she feels that she'll be more comfortable about it if is was with a woman. She tried talking to him and she is tired of pleasing herself. What should she do?