boyfriends baby mother is causing drama

I have no children and so i think maybe i am not able to see things from her perspective and maybe that's one reason we have so much drama but i dont know, anyways here is the story: my now fiance and i have been together almost 2 years. at the beginning of our relationship, he cheated on me with this other woman and got her pregnant.i was able to forgive him and we began to move forward with our lives. the child is now 7 months and the babys mom HATES me. i have been trying to get a meeting with her to try and talk out some issue but she refuses to meet or speak with me. she calls him constantly and i dont like them talking on the phone at all because when she calls, its never about the baby she always begs him to be with her. she always tells him how the baby needs a stable home or she will bribe him with money. i offered to be a middle man and she would call me with issues concerning the baby, he liked the idea but she refused of course. she lives 2 hours away and he goes up there one weekend a month and spends time with the baby. sometimes he wont even tell me hes going, he will just go up there to see the baby and tells me when he gets back because he knows i will get upset. i dont like him going alone and for good reason. this woman will do anything to be with him. she bad mouths me to his mom, and to him and i feel like he never stands up for me because he thinks the best way to keep the peace is to try and please both of us, but i tell him he cant please her and me, one of us is going to end up upset and since im his fiance, i shouldnt be the one. she told him that if he ever brings the baby around me she will cut my hair, beat me up, slash my tires and everything like that. i just want things to be civilized but she wont even compromise. i believe shes mad because he chose me and not her. what can i do?