Как правильно писать: *вечнонезабытый* или *вечно незабытый*? *Вечно неженатый* или *вечнонеженатый*? Similar question for words with this structure. 

I know that, e.g., *вечнозелёный* (the word doesn't have *не*) is written as one word, although I am not sure if it is an exception of sorts.