I have had this mandevilla since June. When I bought it, it was slightly fuller and the leaves were a deep green (darker than it is now). A few weeks ago I noticed parts of it dying off, leaves were yellowing and some of the leaves had red spots or red around the edges. Now it has been pruned of all dead parts and looks sad...

I have it in a fairly large pot (17"Wx17"D) because I am planning on moving it indoors during winter.

It gets full sun for the majority of the day.

I had been watering it often and sometimes after a heavy rain would dump out excess pooling water from its built in reservoir (if I notice it's been sitting for a day or so).

I have not seen any pests other than gnats near the soil.

2 possible factors I can think of:
- We did have a few days/nights of unusual cold summer weather (70F day, 60-50F night)

- My BF perhaps fertilized it too often (possibly a couple times a week) :(

Like I said, it was beautiful and lush with dark green leaves and healthy pink flowers, climbing up the trellis and then it started to decline. We trimmed off all the sickly looking parts, I have been watering (no fert.) it every other day, or as needed. Anything else I can do? Should I just let it run its course? Repot it?