Most of my tomato plants are doing really well. But the one in the cage highlighted in red started failing a few weeks ago. I fertilized with some Miracle grow I had lying around and it didn’t improve. Then I got some Tomato Tone. That did nothing. The plant kept getting worse and worse and now it’s just a husk. I’m afraid blue is following next and I’m concerned about purple. Here’s another angle for some more context. 
.
Any thoughts?
Check the roots, you might have pests eating the roots. Could also be too much watering. Hard to say from photos but I definitely think something is wrong below the surface
I water almost every day. How do I know if it’s too much?
When it shows signs of over watering, they only need about an inch a week after being established. When they are new or transplanted water daily for a week, than give it an inch of water a week. If it rains an inch, you’re done for week unless it’s stupid dry and starts showing signs of needing water (obviously).
You could always get a moisture probe. I’ve found it extremely useful