Fading watermelon

Hello!

Please, help me to find out what's wrong with my watermelon plant (Sugar Baby)... It's in a container now (I only have a balcony), which I know is tiny but I've got another one of the same variety that does very well in the same container size...

The one on the picture looks nothing like the lush green little beauty it used to be... It started to fade and dry out about 2 weeks ago. Now almost all the leaves turn yellow on the edges, and then brown. The vine is very dry and loses its leaves.

Even the young leaves have some kind of yellow discoloration (see 3rd picture). 

Since it's the edges that really become yellow/brown, I thought it would mean the plant is stressed (rather than infected by disease/pest), but I don't exclude mildew either, because some other close watermelon plants have mildew. I sprayed some fungicide (baking soda mixture) just in case.

A fruit was growing but burst open a few days ago .  It was the size of a plum when it burst. So probably it had too much water. I usually water every 2-3 days but I stopped since the fruit burst. The soil is lightly moist now.

I cannot see that I will have more flowers... The ends (that carry the buds) look all dry. 

What can I do? Maybe put it in a bigger pot to begin with? (It's not root bound yet). Or is it really dying? What worries me is that even the young new leaves don't look that healthy (they have yellow dots...)

I also have a stupid question but hey, I'll just put it out there: since we are already in august, even if I get new flowers (which seems unlikely at this point), there won't be enough time for maturation before temperatures drop down (I expect the temperatures to go below 12 degC at night in mid-september). So in case I have a new fruit growing, it won't survive outside in the end of september. Has anyone tried to bring indoors a watermelon plant (with fruit) when autumn comes? (assuming the plant was always in a container). I know it sounds stupid and pointless, but I was really sad that my watermelon burst, and I want a second chance this year  Anyway, that was a side question, I'm mainly interested in knowing why the leaves become yellow/brown and dry. 

Thanks a lot for your help!