No, there is no any special low which can provide you with visa if you are not married with your fiance, even you have common children. You can come to Russia to marry and make permission for temporary residence without quotas for three years.

Ja rod.v USSR,v TBILISI.V RUSSIA rodnix net.

No, you can not to get Russian citizenship. Married - is not reason to getting RF citizenship. At first, you mast to get permission to temporary live in Russia. In a 3 year you can to put in an application to accept RF citizenship.

He has not 2 nationalities. Betwean Russia and Greek not signed agreement about 2 nationalities.