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What Makes Tomato Leaves Twist or Curl - How do I treat tomato leaf curl? (tamu.edu)

Leaf roll on tomatoes can be grouped into one of three reasons:
Physiological- response to heat, water, wind
Chemical - response to herbicide residue/drift
Disease - response to host of tomato viruses

Leaves curl up to protect the plant from losing moisture in extreme weather conditions. When curled there is less surface area to lose moisture, leaves may become thicker as well. As the plant gets bigger, the root system expands downward and laterally. It is the lateral roots close to the surface that also lose moisture. The plant loses more moisture through the leaves than it can take up from the roots. Leaves curling is a response to this and acts as a protective mechanism. In severe cases flowers may drop. Plant leaves and stems generally remain green.
Thoroughly water the plants at night close to the stem, avoiding any soil splashing on the plant. Look at them in the morning. If they look better, then you have ruled out a viral problem. A shade cloth purchased from your local garden center will help with this issue.

When leaf curl is caused by herbicide drift, the leaves will look like a cup and the stem will be bent downwards. The leaves will be yellow/brown but only the ones affected during the herbicide drift. In this article, Figure 3 shows the same symptoms as I see in your photo.
Herbicide Damage in Tomatoes | Mississippi State University Extension Service (msstate.edu)
Questions to be asked if this might be the cause: what the container was used for before planting the tomato; was the soil contaminated in any way; was the plant near a farm field or neighbor's yard that had applied any herbicide. Protecting tomatoes from herbicide drift - MSU Extension
I do see that your plant has the leaves rolled upward, stem bent downward and there is some chlorosis occurring on some of the lower leaves.

The last cause of leaf curl is any number of tomato viruses, none of which have good outcomes. When this is the case, the leaf color is involved ranging from mottled yellow to internal browning.
The top three are: curly top virus; tomato mosaic virus; and tomato yellow leaf virus.
Curly top is a systemic virus brought to the plant by leafhoppers. Infected plants should be removed immediately - encase in a black trash bag, cut off at the base, leave the plant tied off in the bag for a day in the sun. This should kill any leafhoppers and throw the plant into the trash.
Curly Top Disease of Tomato | Oklahoma State University (okstate.edu)
Tomato yellow leaf mosaic virus is brought in by wind/rain/other environmental carriers. It causes mottling of the leaves and internal browning. There is no preventative and no control. It can live in the soil up to 2 years. Plants should be removed and thrown in the trash.
Plants infected with tomato yellow leaf curl virus, show marginal leaf yellowing, upward or downward leaf cupping, smaller leaf size, flower/fruit drop, and the plant's growth is stunted. It is spread by whiteflies. Spraying NEEM on a regular basis, helps to keep the population of whiteflies down. But again, once you have it the plants need to be removed and thrown in the trash.
Tomato Yellow Leaf Curl / Tomato / Agriculture: Pest Management Guidelines / UC Statewide IPM Program (UC IPM) (ucanr.edu)

What Makes Tomato Leaves Twist or Curl - How do I treat tomato leaf curl? (tamu.edu)

Plant & Pest Diagnostics (msu.edu) may be able to properly identify any of these diseases.

   You are wise to have separated this plant from the others. It appears to be mostly healthy but your statement that it is getting worse is not a good indicator of a positive outcome. If you had a disease issue from any of the above diseases, other plants would have been involved. If the stunted growth was from herbicide exposure, the fruit should not be consumed. If the plant has not recovered from its leaves curling I would destroy it and place it in the trash not the compost.