I’ve said this before on here, but bears repeating as I don’t know that everyone realises you can do it - a great way to wean yourself off the Facebook checking addiction is to unfollow all your contacts and pages. Once you do this, your homepage is basically blank (no news feed), but you still retain the ability to use the messenger, which unfortunately is still socially quite useful from time to time despite having a horrible UX. You also maintain the ability to access pages as usual (FB aggressively tries to push you to register if you view them logged out) and get notifications if people tag you.
I’d really recommend trying it if you have the same feeling of wasting time as the OP - it’s a bit less drastic than removing your account, but it does the job. I thought I might refollow certain people after a while but six months later I haven’t bothered and I now only check the site once a day for messages usually.
You can either do the process of unfollowing manually, or using JavaScript - there is a settings page where you can list all your contacts (by pressing load more a lot) then automate clicking “unfollow”. I can try to find the script I used if you are interested. Sounds like another option is to use a browser extension.
Another piece of advice that others have mentioned is to delete the app - if you want access messages, you can use mbasic.facebook.com. It really sucks that they removed messaging from the mobile site to push users to their sucky apps.
I’ve got respect for people just deleting their account but for me messenger still has enough social use that this is a perfect compromise for now!