The bug is a leaffooted bug.  The damage is similar to stink bug damage.  The bug mostly affects the fruit.  The insects have piercing-sucking mouthparts and puncture fruit or seeds to suck out plant juices.  The bite of the bug causes yellow speckling on the tomato when it is ripe.   The opening left behind can allow access to secondary invaders or rot.

 Leaffooted bugs are common pests of tomatoes and potatoes, rarely causing damage on cucurbits. Bugs are large (to about 3/4 inch), browinsh to gray, with backs flattened and shield shaped. Hind legs are prominently flattened. Feeding damage causes speckling and spotting of tomato fruit
 https://aggie-horticulture.tamu.edu/vegetable/problem-solvers/cucurbit-problem-solver/cucurbit-insects/leaffooted-bug

Best Ways to Control

There are three ways you can manage these insects:

• hand-picking (be sure to wear gloves if utilizing this method),
• sucking off the plant with a hand-held vacuum,
• spraying plants with pesticides. If choosing to use a pesticide, read the product label and make sure it can be used in the area you are treating (i.e. vegetable garden).  Once they are adults spraying is not very effective.
• https://travis-tx.tamu.edu/2021/08/23/leaffooted-bugs-common-in-summer-vegetable-gardens/

The bug is not the cause of the rust and yellowing of the leaves.  The yellowing of the leaves is probably due to a nitrogen shortage.  It also looks like your plant has spider mites, possibly one of the wilts, and/or a fungus.   It is time to take the plant out.   Even health tomato plants rarely produce fruit this time of the year.  Our tomato season is usually over in June.

When you take the tomato out put it in the garbage.  

Jim, Larry and Leslie