Help with my suicidal depressed ex girlfriend?

I really could use some help. Im 22. I had been with my ex for 3 1/2 years. The whole relationship was typical for a teenage relationship. Good at first and horrible towards the middle and end. I never broke up with her or even asked for a break as I felt deeply in love with her. She broke up with me countless times and even got a new boyfriend for about 4 months. I had no trust in her but simply couldnt leave her. About a month ago I finally got the courage to break up with her because of her marijuana habit and the way she was acting. I did it more so to deliver some sort of wake up call, to show some backbone. My intentions were for her to change her ways and for us to get back together. However, about 2 weeks later I met a girl and though its only been a short time I really care for her and know for certain she is better for me. She makes me realize what its like to be with a good person you can trust. We have now been together for 2 months but as of late my ex calls me every 10 minutes crying and sobbing, saying she is depressed and doesnt want to live anymore and needs me and has nothing going on in her life. She is extremely in need of counseling and is crying/miserable on a 24/7 basis, claiming her life is horrible and she "is going crazy". She is literally begging me. I love her but know I need to let it go and stick with the girl I am now with, and even if it doesnt work, I know my ex simply is not the one. What can I/should I do to alleviate this situation. I feel like I cant say things that will hurt my ex for fear of making it worse on her but I am in essence providing false hope. Any ideas? I could really use the help. Please help me.