URGENT! I need some advice on what I should do

Hello, I have never asked a question on a forum before but I really need some help.

I am currently in a relationship that hasn't been very long and it is my first for about a year and I am unhappy. The girl I am with is a really nice girl and I really like her but she is not on the same boat. An ex girlfriend I never got over and we separated for an understandable reason. I have wanted to get out of this place I live in for a while. My ex-girlfriend has a child and I have always loved her, and she told me she still loves me and has offered me a new life.

I don't want to hurt anybody because I know I'm actually a really nice guy and I know that what I do is going to hurt someone.

What is the best advice I need right now?

Stick with your new girl, your ex is used goods sorry to say.