So frustrated

My fiance doesnt discipline his 4 year old son he let's him hit me and call me names, he let's him swear and throw things, I have never seen a worse behaved child in my life...I honestly dont even know what to do anymore cause he doesnt listen to me when I tell him that he needs to discipline him I give him ideas of how he could do it and he just refuses..I'm so frustrated and very upset right now