Change of Status B1/2 to J2

Dear All,

My fiancee is currently studying in USA and we are planning our wedding with in next couple of months, due to importance of her studies i will be staying in USA with her for the duration of her studies.
I am dual national i have a B1/2 Visa and i am also a British Citizen.
The question i have is i am aware you can apply for COS in the US to J2, if i do COS what will happen to my Visitor Visa?? will it be cancelled or remain valid?? secondly how they perform COS?? do they stamp the visa or any other method??? if they do not stamp the visa how i will be able to travel in and out of the US??
Do i have to renew J2 everytime i leave US??
Does COS effects your eligibility in the near future as in they may think you tried to stay in the US and perform COS so your intentions are to stay in the US?
I will appreciate if someone can answer this which will help me make a decision.