Boyfriend deported, can he come back as my fiance?

Hi, my boyfriend was deported to Mexico a few months ago for being in the US illegally . He was brought to the US when he was 2 by his mother. He got caught driving and was charged with a DUI, and no ID.. other than that, he has no other charges against him. He signed voluntary deportation papers.. then got deported. He is 22. I wanted to know what forms i/he can fill out, if any, to bring him back to the US. We were going to bring him back on a K1 visa..but then found out his status is "deported". Can we still fill out the K1? or is it easier to get married in Mexico, then try to bring him back? Thankyou.