What should i do when my husband wont get rid of his best friend, whom is interfering with our marriage?

me and my husband have been married for a year and 3 months now, we're pretty young, 18 and 19, and we have a one year old son. we've had our share of hard times, but we've decided to do what it takes to make things work, and we're doing really good now. hes in the army, stationed in korea, and im in the states. the only problem is his best friend, whom i use to be friends with, keep bashing our marriage and tellig my husband he shouldnt be with me and he should cheat on me. he also plans to move wherever the army sends us, to open up a shop wih my husband. my husband claims hes not listening to him, but is steady comming up with the same plans as his idiot friend n trying to conviece me is not about his friend. also this friend of his has two kids by my sister, and dose nothing for them or my sister.so hes a dead beat. i told my husband im not happy with his friend bashing us everyday, and i dont plan on living our lives wth him in our shadow, but he wont cut him off. what should i do?