I need to know I've applied for immigration petion through my brother who is a citizen but I am engaged to get married to a US citizen also. Here is my ? If I get married will it afect the application that is ongoing with my brother?

Go here http://www.immihelp.com/ register and you will get your answer for free from immigration experts. Or email the US consulate handling your case . If your not In the United states email the US consulate in your home country.