Not marrying fiance

[immihelp]

Sir.

I want to know what happen if a man received fiance visa and entered in US but due to some personal reason they will not get marrige with each other? Either man can get marrige some other US National girl or his fiance's sister?

Please help me if you know any provision in US law?

[immihelp]

No, you can't do that. If you are not marrying the fiance, you must go back and start all over again.