How to obtain his residence card?

Me and my boyfriend has been together 2years this March. We have a Bby he's 13 months old and I'm pregnant again with his 2nd child. We want to get married but I'm scarred if we go to court and try to hell get deported he was born in El Salvador but came here wen he was 17 he has a valid pport also. If y'all know anything that can help us out in getting married in Texas,or will he get deported if we try to. I also want to marry him so he can get his residence card because if he get deported my boys will be without him and I just Dont want that to happen.