All spurges - Euphorbia species - want very well draining soil and minimal watering after establishment. And most want full sun. Other than that, I can't tell much more......it is possible that a single plant can have issues after planting. In fact, it is fairly common for a multiple planting of the same species to perform inconsistently.

Thank you!!!!! I think I overwatered it Sooo I'll stop that and keep my fingers crossed. I also turned off the sprinkler system hose that runs the length of that area. Same with delphiniums? They aren't as bad as that guy but aren't exactly thriving. Thank you so much for the help!!!! So much mixed info out there on the web, especially for our unique climate, and I've been just trying to follow the advice of the nursery I went to (O'Tooles) but I got so many different plants that day that I think I'm mixing up the advice. Note to self: next time write it down! THANKS!!!!!