My mother is getting married to a guy she just met a month ago! please help advice?

hi im 18, and my mother is getting married to a west indian guy he is from Trinidad, she just met him a month ago, the only reason why he is getting married so he can be a citizen and he can work, someone told me it was called a green card. my mother and i really dont have a good relationship like i cant go to her and talk to her about things that go on in my life, we never had a mother daughter relationship, my question is how do i treat the guy she is marrying i dont want to be rude or disrespectful, i have no problem with them getting married, i just think he is using her to get a green card. any advice how i treat this man once he is married to my mother