Since you purchased your plant from our Native Plant Sale (thank you!) we don't have to ask any questions on whether the Capsicum annuum (Chile pequin) in your garden is native to Central Texas.
Some of the members of this genus are annuals, but they should not begin to die back until October, at the earliest. Since other plants around this plant are doing okay, we will have to hark back to the only change in conditions you identified, which was the move from a pot into the ground. Since this plant can tolerate sun, part shade or shade, it would not seem that the amount of sunlight available should be an issue.
The first thing we would question is the fertilizer: most native plants need little or no fertilizer because they have adapted over centuries to local conditions. In fact, some native plants are actually opposed to fertilizer. Second, if you follow the plant link above to our webpage on this plant, you will note under Growing Conditions that it has low water use. Three times a week, even though we have been having some more rain than normal in Central Texas, is probably excessive. We think you have been giving that plant too much love.
There is also the possibility of some root damage when it was transplanted from the pot. Since this species is annuum, it probably doesn't have much longer to live anyway. If you managed to harvest some seeds before it began to dry up, perhaps you can reseed for next year. Propagation Instructions are on the same webpage.