How do I repaint this?

All sheet goods should have primer before painting. Kilz or Zinzer work well. Bathrooms need a latex enamel paint and not a flat paint. Moisture is the enemy. Fan or open window should be used during showers or baths to get rid of moisture.

I really think.you have a moisture problem on that wall. Are there plumbing pipes behind wall? Outside wall? Chimney ? That's not normal. Do some investigating. So sorry for your problem.

Every wall has this green board. Earlier posts said I could use diluted latex paint as primer. Did that ( in some places I had already pulled off the paint) and for the most part the paint stuck. Few small bubbles. Already have the paint and it is latex FLAT to help hide the uneven wall texture. No money to put into the room as it is very large. Yes, moisture was a problem. Installed a window as well as using fan. Any more ideas. No budget for Kilz or Zinzer, though I would use it if I could.

Ive used pool liner as a wallpaper it works great...just passing on the idea..

Sorry but there really isn't a way to avoid this happening again if you can't seal (prime) the board to keep moisture out of it. You can make sure the drywall is completely dry by not using water in the bathroom for a few days then paint it really well with your paint then let it dry completely again before introducing moisture. That will help but they are right that flat finish paint will allow the moisture to penetrate it again. Sorry

You need to prep the walls before doing anything. Make sure what paint you use to cover is compatible with what is already on the walls. My aunt repainted her ceiling, and her ceiling crackled, which was not her intention. Need to check for any leaks. How powerful is your vent? Good luck.

In order to stop what is happening again on your walls, you need to stop the underlying problem. I would say there's a moisture problem making the paint blister and flake. Figure out how to stop that.

Preparation is the most important part of painting. Please save for a good quality primer. Scrape, sand and prime your walls then paint- And yes, a latex enamel or similar is used in a bathroom for a reason. If you don't do it correctly, you will continue to have these problems.

also buy paint that has primer in it already

Looking at your pictures, it appears you're down to the green board in many areas. Besides being very sure these wall boards are dry through and through. If a dehumidifier is available to use or borrow, suggest using in that room for a week or so (it takes a long while to bring a room to low humidity level in FL). Once that's done and as much as you can lightly sand away the green board paper and whatever else is mucking up the surface, skim coating with dry wall mud can work wonders. Once you've done the skim coating, let it dry thoroughly then sand down any rough areas or high spots. You should be able to follow with prime and paint and have no surface failure. The key will be super dry board to work with, very thin skim coat of dry wall mud and meticulous prepping over all. Good luck!

Black mold can be dangerous. You need to be sure that is ALL GONE before you skim coat.

I have used paint with primer and it does not do a good job. Ken has the right idea. Your enemy is excess moisture and once you resolve that issue the paint will hold providing you use the right application. Good primer, Zinsser Bullseye 1-2-3 and then an enamel. If you should ever decide to repaint with a latex paint in the future you will have to reprime before doing so.

Sand it down level and then apply Kilz. Kilz will put a barrier between the wall and the paint/ wallpaper/cement.