Question on adoption?

my children's father has been out of there lives for almost 2 years now he was deported me and my fiance will be married in a month he wants to adopt my children does any one know how i can start this or can i even go through with it if i cant get ah-old of him he was deported and bard from the usa for ten years he has not called or any thing to ask about him children my fiance has been the one here with my children for the last year and a half im not for sure if he can adopt them and give his last name to my children without the consent of the birth father but like i said i wouldn't know how to get ah-old of him or anything about him and he has been an absentee parent for almost 2 years how do we go about this