Maybe I should leave

I am lost in what I should do. My childs father and I have been together for almost 2 years and things have been very rocky. besides the cheating that he has done continuously, he swears he's a changed man. Deep down I really feel like he hasn't. Other than that he let's his sister disrespect me. let me start off by saying that me and his sister was OK with each other first. Then this girl leaves a heart face on his post so I asked her what was it for and she just started going off. Her and some more women. Then his sister was laughing at everything the girl was saying and I'm confused cause I'm like "wtf is so funny?" then come to find out she has told him that she doesn't like me. so whenever we get into it she blames me and he says nothing. he let's others disrespect me and doesn't open his mouth. Now I have a question. Female or male, should your man stop someone in their track if they disrespect you.? This goes for family as well. because its been times where me and him would argue and he say mean things and I would too then next thing I know is his family or mainly his sister would automatically assume I'm bothering him.