Bf let step sister disrespect me

So my bf Let his step sister send me a disrespectful message after me and him got into an argument when she was around and wasn't minding her own business when we were trying to talk privately. I told him about it and sent him a screenshot of the message and he said it didn't seem that disrespectful for him when this girl was talking about my past trauma (which my bf told her about without my permission as it's my business), she talked about how I'm insecure with myself, and she even talked about my body count.. My bf seriously seen nothing wrong with what she said to me and honestly I feel so betrayed by him. I asked if he stood up for me and he said he just asked why she texted me and I was like that's it? I blocked her right away because I'm currently pregnant and don't need her drama. I just don't feel like I can be with someone who can't even stand up for me over someone else. This girl isn't even really his family her mom has just been dating his dad for like 7 years and they're not even married so I don't even classify her as his family but he does. I just don't think I'll ever look at him the same because now I know he wouldn't stand up for me if anyone talked down on Me like she did.

@mommaof4 she was saying nasty things to me not giving me unwanted advice. I guess because she didn't like how I was arguing with my bf when it was none of her business at all.

@Niki I've been with my bf over a year and he's never even introduced me to this girl and I've never talked to her before. I didn't talk to her at all because he wanted me to come over and talk to him and I didn't even know she was going to be there. I have met literally everyone in his family (even this woman's mom) but her. I'm a very respectful person. Our argument had nothing to do with this girl. I'm a 34 year old woman and I'm not for drama that's why I blocked her right away instead of writing her back like I'm sure she wanted me to considering she's in her early twenties. I don't even know why he told me to come over and talk to him if he knew she was going to be there. I don't even know why he's never introduced me to this girl considering I've met everyone else in his family. She had absolutely no reason to message me even if he talked to her about our argument. It's childish.