I got separated from my ex in June 2007 , we were living together common law. I purchase a house with him that he now live in , I want to know if he change the locks on the door and moved in is new girlfriend with all her stuff . If I am hable to do something about it , nothing have been legally separated yet between us and some of my belonging are still there mix now with her . As he have the right to do everything he wants

You could take him to court, but a court might ask you why you waited so long and you might only get your clothes and personal property (jewerly, make-up, etc... and maybe anything you could prove was solely yours) back if you are lucky. When you leave the person only has to keep your stuff for a reasonable period which I don't think is 7 months.
Since you were not married they do not consider you entitled to as much rights as if you were married.

Have you told him you want your stuff back? What does he say?

Your only other option is to call the police and ask them if they can escort you to his house to get your stuff.
People that I know that have done that said the police only gave them 15 minutes to get their stuff.
So if he is willing to give you your stuff it would be nice if he were helpful enough to bag some of it up before hand.

lucy525 writes: "I purchase a house with him". Get a copy of your deed and see if your name is on it. You have the right to get your things out; you can meet with a magistrate of justice of the peace and discuss your options; take an adult with you so you can both review the information that you hear. Better yet, if you are on the deed, then consult with an attorney about your rights and liabilities (mortgage, insurance, taxes, etc.).