난 너를 못 잊을거야. is correct. 난 너를 못 잊혀질 거야 is wrong because "잊혀질 거야" means "will be forgotten." 너는 못 잊혀질 거야(You cannot be forgotten). is grammatical, though it sounds weird and people don't say it.

You shouldn't use the passive form 잊히다/잊혀지다 after the object 너를. It should be an active form 잊다. - 난 너를 안 잊을 거야 = 난 너를 잊지 않을 거야 = I will not forget you (I will intentionally remember you). - 난 너를 못 잊어 = 난 너를 잊지 못해 = I can't forget you. (more of a natural state than intention) - 난 너를 못 잊을 거야 = I think I can't forget you. (same, except it is weaker and more about the future). - 너는 (내 마음에서) 잊혀지지 않을 거야 = You won't be forgotten (in my mind). * Note the different subject and no object.

It has different meaning between the two sentences the first one meaning is i will not do this now and then with My desire But the second sentence like i want say to him it’s out of my hand or i have nothing to do

It has different meaning between the two sentences the first one meaning is i will not do this now and then with My desire But the second sentence like i want say to him it’s out of my hand or i have nothing to do

I think "I'll never forget you" is better.