It is not religion. I am a Muslim, but I was born and raised in the US, and I am very assimilated. One major issue, though, is that Muslims put a lot of their identity into their culture.
Islam is not a culture specific religion, and is very adaptable to almost any culture. I have no problem being a devout Muslim in Western society, and neither should he.
Another thing, (at least with Arabic culture, I don't know if he is Arabic) is that family is a major factor, and because of the way the Arab, and Muslim world views the west, his family might think you are a bad person, simply because you are from the UK. (The UK has really messed up middle east over the last 200 years, so you can see where it comes from). His family might be putting stuff in his head, but you can't really confront him about that.
Honestly, I think this is very much a culture clash, and not a religious one. What you are saying you are doing is very much within Islamic law. Islam says a Muslim can marry a non Muslim, and their only obligation is to teach their children about Islam, and let the child decide.
Also, he's not being a very good Muslim, because a Muslim man must treat his wife with respect. I suggest to you, to read the section of the Quran titled "The Women". It's all about how a man must treat women, and when he starts going against it, point out how he is being a bad Muslim. With the Quran as your proof, he can't really argue.