Is there a drainage hole in the pot, and is it plastic or metal? How long's it been in that pot? Is it suffering from drought? Does it get more sun exposure than your other plant, if they're in the same type of pot?

It's in a pot which is far too small for it (whatever the pot is made from) and it's planted too low in the pot. It needs to be in sandy/gritty free-draining soil and if you have to water it be sure to water the soil and avoid getting water on the leaves.
It should be enjoying this spell of hot weather.