So I started dating this new guy and we have been together a monthe and I can not leave the house with him without her going I'm not sure what's wrong I tell her she can't go and she throws a fit and crys I need help what's going on with her?

With this limited info,

1. she sounds like she is jealous of the relationship
2.or she does not want you to get to close to him.

Have you sat down and asked her ? Or have you just left and let her cry ?

I agree with the other answer. How you respond to her is going to make all the difference. At 15, she is old enough for you to sit down with her, without him around, and find out her reasoning. That will determine what you do next, but 15 is also old enough to understand that you need companionship. But you should reassure her that you don't want to leave her out, or forget about her. You need to find out, from her, what she needs to from you so she will be comfortable with the relationship.

That actually happened to me when I was in that situation with my mother. She started dating this guy, and I really needed my mom.And your situation could be totally different, but she just wants to feel like she is more important then him. Like when you guys go out the just the two of you, she feels as if you want him more than her. So I would suggest that you dedicate one day of the week to spending with your daughter. Like every Tuesday after school you guys go out to eat or a movie. Just let her now verbally or with some sort of dedication that she is more important.