My first guess would be burn/dehydration from going inside to outside. Did you harden the plant off before moving it out and how long was it outside before this happened? If the damage appeared shortly after the plant got it's first bright outdoor sun, it's very possible that the sun burned the leaves and the wind cause even more burn/dehydration and broke up the damaged/weakened lead tissue. If this sounds likely, I would recommend moving it to the shade and also trying to get it a bit of wind protection until it strengthens up, then exposing it more gradually/progressively over the course of a week or so to that hot TX sun.