My Rhododendron is going to prematurely depart?

Hello,
some weeks ago I bought a wonderful potted "Marie Fortie" rhododendron ... but it has soon become sort of a zombie: the flowers have completely rotten and disappeared and the leaves have first shown brown spots and then have almost totally fallen.

Just to keep it short this is what remains of my poor Rody:
(I swear it was amazing when I bought it!)



I've read something about a nasty fungus called Phitophthtora which should be treated with sulphur (?), so I tried with copper sulphate... but it got is even worse: now it has almost no leaves left.

What do you think I should do (except a funeral, of course)?

Do you agree it is actually Phitophtora or perhaps those ugly brown spots may be sunburns (I am afraid I kept it on a balcony exposed to the scorching sun of Rome for at least 2 weeks...)?

Thank you in advance and... ok, sorry for my poor English!

Here are other disturbing picture of my poor rody...

 

I think it has got waterlogged and the poor thing has rotted. Take it out of the pot and check the roots.

 

In fact I'm afraid I gave it too much water, too.
I'll do as you say. Thanks