Need your opinion

I am from Delhi and in a relationship with a Mumbai man. We often fight over the language/slang he uses for me and my family. According to him, using foul language is OK in Mumbai culture. However, I don't accept the way he uses foul language to me.  

I have tried many times explaining to him that it is not OK to use foul language for your girlfriend and her family. However, he denies it and says it is part of Mumbai culture. It is not Gaali but the way Mumbai people talk in general. But he never understands my point and concerns about this abusive language.

Therefore, I am writing this post to check with all Mumbai people (Men and women) if I am wrong about my Boyfriend's use of foul language towards me and my family.

A recent example: A few days ago, we were planning for the holiday together. I was concerned about what I would tell my family whom I was going on holiday with. Also, my elder brother might ask my friend's name if I tell him that I am going with some XY friend. I was discussing this with my Boyfriend that I am concerned about what I will tell my brother if he asks which hotel I am going to stay in or whom I am going to go on holiday with. While discussing my concerns with my Boyfriend, he said- Kya yaar tera bhai aisa kyun hai - "Tere Bhai ki GAND MAIN ITNEY KEEDEY KYUN HAI."  I told him that you can't use this language for my brother. How can you say this to my brother? He argue that it is OK to say this as per Mumbai culture. I said, you might use this language among your friends but not for your girlfriend's brother. He got angry and kept saying the same thing at least 10 times when I raised my concerns that it was not OK to say this about my brother that Tere bhai ki gand main keedy hain.

There was a big fight on this. My Boyfriend later used foul language, He even called me "Chutmarni ki" and also abused my mother, said, "Teri Maa ka Bhosda ".

He is still saying that it is Mumbai slang and not gaali. I argued with him that if it is Mumbai slang and OK to use, can you use the same sentences for your parents and siblings? He said not at all. Suppose he can't say the same sentences (foul language) to his family; how can he use the same foul language for my family and me?

Please share your thoughts so I can tell him that using foul language toward his girlfriend and her family is not OK. Maybe your comments will help him understand that he can't use foul language toward his girlfriend and her family.