Congratulations first of all on the pregnancy!
I'm all for optimism but I'm afraid I will sound quite negative. Your first fight will be your acceptance and recognition of his family. Yes, you have spoken to his mother, thats one thing, whether she and the rest of the family will be happy to see him marrying you is another. You'd think they would be quite happy to marry Westerners but its not really the case (am married to a Nepali). Anyhow, getting them to accept you is one thing, another is to accept you being pregnant and married. I know that in my situation it would have been a big no. Hubby's family are not that strict but the shame it would have brought upon them, not only to be married to someone outside their culture but for this girl to be also pregnant. Impossible.
I'm assuming his parents live in the UK? If not, he may live here now but as he gets older, he may also have to look after his parents which could mean you will all live together, in India?
The other thing is, to me, your relationship doesn't sound very stable to begin with. You will face some cultural difference so if you are not strong together, you will really struggle.
Of course I don't know anything about your partner. I don't know his religion, how strong he takes his faith. It all sounds so romantic in the beginning, Indian food, some aspects of the culture are very enticing but its not all Bollywood glamour. How and where will you live? How involved will his parents be? How free will you be to make your own decisions after marriage. How will the child be raised?
Of course you could have a wonderful marriage but I just want you to really think about it, think of the complications and how you will deal with them. You already don't trust each other, doesn't sound like the greatest start.
Sorry to be so negative, I hope it all works out well for you.