ever==adv.1) always; 2) at any time; 3) in any way: AT ALL;
forever==adv. 1)for a limitless time; 2)at all times:ALWAYS;
I will not forget it forever.我將永遠不會忘記這事;
I will not ever forget it. 我將無論如何不會忘記這事;
參考: Partly according to ”The New Merriam-Webster Dictionary 1989”