Why is everything I post on Facebook going to my messenger page

That would be a good question for the very helpful folks at Facebook support.

ethelfromshelby wrote:

Why is everything that I post on Facebook going on my messenger page

We would have no clue why. Apple wouldn't know why either. This is a user to user only forum and Apple doesn't own Facebook or Messenger. Meta does, so ask Meta why would seem what you need to do for an answer.