No, however, if you look you may find some small obscure country that allows this. The laws recognizing marriage are universal in all Western countries and therefore you would not be able to legally marry him in them if he is already married.
My Boyfriend Is Married In Mexico, Can I Legally Marry Him Here In A Different Country?
I was married in the US to a mex icon national and am now living in mexico with him is may marriage legale in mexico
No, in the US it is illegal to be married to more than one person and your marriage would not be valid.