I wish you had given your age, because that's critical. I assume both of you are young adults?
If so, the one obvious truth here is you and your bf were nowhere near ready to discuss marriage. If you were, the religious differences wouldn't even matter. The 2 of you would discuss it, come up with a plan on how to raise future kids, and that's the end of it. Parents don't matter, because this is a decision between a man and his future wife. I happen to love my inlaws, and we're very close. But when I got engaged, it was understood we made our own decisions. For some reason (probably age) you don't have that yet.
So it's very possible he isn't drawing good boundaries with his parents. However, it's also important you see what you've done wrong here. A woman ready to get married doesn't created FB drama with future inlaws. Your mistake wasn't that you didn't ask your bf about it; your mistake was that it occurred to you in the first place. It was also immature of you to text them saying you want to discuss all this. The discussion should be between your bf and his parents.
As for what to do next, odds are high this has run its course. But if you're determined to give it another go, think carefully about how all this played out and then talk to him. Make sure he understands that the 2 of you started making plans you weren't ready for, and if he wants to continue the relationship, both of you have to take a big step back. Even typing this, though, odds aren't in your favor. The important thing is for you to learn from all this. You said a couple times that things were good in the beginning, but this is pointless. Things are ALWAYS good in the beginning! As time went by, both of you started seeing problems and red flags. The other risk, if you're young, is that both of you are still growing and changing while all this goes on.