My Torenia appears to wilt and feels a bit tacky.
Certified GKH Gardening Expert
It is likely being affected by insect pests - perhaps aphids or another sap-sucking insect. The stickiness is from the honeydew these pests leave behind. I recommend treating the plant with Neem oil, which will help take care of these pests and many others. Here is more information: https://www.gardeningknowhow.com/problems/pests/neem-oil-uses.htm