How to break up my ex-gf of ten months with her new "boyfriend" who isnt official, and who i dont know?

How do you know he is using her if you know nothing about him? Basically, you called her and told her how you are now. That is all you can do, is leave the door open. Don't force, but let her know that you are there and care. Don't act desperate. Act as a friend and someone to talk to, and maybe she will come to you. If it's meant to be she will realize. Good luck!