This is a bit late, but your viola appears to have behaved quite normally--they are not usually all-season performers in warm climates and tend to wear out as the temperatures climb. The plants are also not particularly long-lived, if they do survive longer than one season, which they often don't. You might be able to cut back the lanky stems to improve the plant's appearance, but you should not do that unless you can see healthy new growth sprouting at the crown of the plant. The plant may also simply die out altogether after producing seed.