Could anyone tell me if this dying ?
That looks like it got hit by a frost...maybe give it a cover of fleece in any evenings that frost is expected. If you trim any dead bits with a bit of sunshine and a light feed should recover. They are tough plants but are not fully hardy.
To Plant a Garden is to Believe in Tomorrow
My Oleander is around 15 years old and has always been in a pot.
For 2 years it got scale insect and sooty mould which I did all sorts to get rid of.Finally I hacked it right back which meant no flowers the following year but it did the trick and is now a lovely shrub.It has never been protected and survived the 'Beast from the East' in 2018 going on the flower the following summer.
With yours I would cut back all the dead branches and possibly repot.Keep somewhere sunny and water well.
Be careful though as all parts of this plant are highly toxic,don't even burn as the the smoke given off is also toxic!
“Every day is ordinary, until it isn't.” - Bernard Cornwell-Death of Kings