My friend and his girlfriend are getting married?

my friend/ex is getting married and they have twins and a little girl who recently had breathing problems and they were sup-post to get married but they didn't an they didn't cancel it or anything and he has cheated on her many time with his ex Stacey. and MANY other girls and is a alcoholic and a stoner and he loves to make love. to all the girls he has been with and then he goes home and makes love to summer. and she STILL stays with him. i have no clue why cause that is just ridicules. what should she do?