How to get those brass fittings apart

Lots of notes at this link:

How to remove garden hose nozzle that is stuck on a hose

.These stand out:

retiredjg:

Boil a big pot of water - in a pasta boiling pot. Carry the pot out to the recalcitrant hose/nozzle. Dip the nozzle and a few inches of hose into the pot for 30 seconds or a minute. Unscrew it. If this does not work, try again using a longer or shorter dunking time.

Masterblaster:

https://www.youtube.com/watch?v=BibpHxS4ako

jharkin:

Usually the nozzle is in pretty bad shape as well and getting it apart requires techniques that may destroy it anyway, so I just cut off the hose with utility knife. Then repair it with a hose mender and a new nozzle...

sam5:

For the future, this situation can be prevented by using pipe tape (white teflon tape) when assembling the nozzle onto the hose, or the hose onto the house faucet.

LifeIsGood:

Be careful using Vice Grips on a soft metal fitting. Too much pressure can deform the fitting making it even harder to remove. I have had great success getting stuck threaded fittings apart with PBblaster. Readily available in hardware, auto and home centers.

So heat, or a saw, or PBblaster, or throw it away. And use teflon tape. Got it.