I lied to my gf and don't know if I want to live anymore
Why in the world would you want to lie to your girl?
I never intended to lie to her in the beginning
You're just being over dramatic. Sit down with your girlfriend and explain exactly how you feel.
Maybe I should use this to my advantage and then get back together with her.
I think that if you are ready to tell her the truth, you should sit down and talk with her. I think that it is good to talk through problems in your relationship.