The picture appears to show a female brass fitting that has jammed on the male hose end. Probably due to galling, which stainless steel is highly subject to. Brass should be resistant, but it's either galling (stainless steel is good enough at it that it may have overcome the brass) or corrosion products from being left attached in the weather for a long time, at best guess.
Or is the male end of the hose going into an Aluminum part? That would be a disaster in terms of galling potential, but the fix would be the same. Not entirely clear where hose stops and stuck fitting starts.
That should be fixable by carefully cutting the brass fitting to release the female threads from the male stainless steel threads, without overcutting and damaging the male threads. I don't think replacing the male end of the hose is practical outside of a factory with all the right tooling on this sort of hose.
Before using again, apply anti-sieze compound to the male threads of the hose before assembling to a female fitting.