Tropicals & Tender Perennials: A very SAD site - Help please, 1 by Eglantyne

Eglantyne wrote:
Hi everyone,
received some cuttings from Shirley last Year and they did sooooooo good until I brought them into the house at the first frost.
The largest one is 4 ft+ tall now ,in a large pot and upstairs in the hallway ,by a window,near baseboard heat.I think I water it enough .
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Well, it keeps on loosing leaves like crazy now and every morning when I come out of my bedroom I see new leaves have fallen.It just makes me sick !! I had that beautiful luscious plant and now THIS !
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as You can see on the picture I also have to battle whiteflies which I sprayed for .
This morning leaves were just hung from the top..limp !

What can I do to save this plant ?
Thanks in advance,
Brigitte