to not understand Christians who have sex/live together before marriage then marry in church?

[onlytwo]

Posting here because I am genuinely confused and not trying to offend anyone.

I keep seeing couples who describe themselves as Christians who have been living together for years, sometimes with kids, then they get married in church with all the religious vows etc. I thought one of the key Christian teachings is no sex before marriage yet it seems really common that people ignore that part but still have a big church wedding.

AIBU to think it is hypocritical?

Because it’s cultural. We are culturally Christian. It obviously doesn’t mean everyone who believes in God and considers themselves CofE reads and follows the scriptures.

My question is specifically about behaviours like premarital sex which are directly addressed in religious texts.

But they aren't. That's the whole point. There are those references to 'fornication' and 'sexual immorality', depending on which translation you are using, but those words are subject to interpretation. Strict conservative Christians interpret them one way, other Christian denominations interpret them another. There's no evidence to prove one interpretation is correct and the other isn't, there's only disagreement.