GAH, I'm sorry you received messages from folk feeing offended. They made it about them, instead of realizing it was about you. I'm sorry they didn't see that perhaps it was causing you anxiety etc. But that to me is the vibe Facebook drags out of folk.
So, good question. I can still use messenger. Which is really handy actually. So i deactivated my old account and I still had the messenger app on my phone and that worked fine.
When I created a new account that I am not friends with anyone on, but am members of groups and interact on some pages, I also have messenger with this and I can flip between the messenger accounts.
Does that make sense?
The drama and politics of Facebook is just too much for my little brain. It really overwhelms me too and becomes too consuming.
Best of luck in building up to shedding it. I highly recommend an account that you just aren't friends with anyone on.