adverb
forever; for good; indefinitely; as long as one likes
Expresses that something continues without end, or for an indefinitely long time. Often used in negative contexts or with verbs like 待つ, 覚えている, 忘れない. Can also imply 'as long as one wants' when used with permission or ability.
あなたのことはいつまでも忘れません。
I will never forget you.
You mustn't wait here forever.
好きなだけいつまでもいていいよ。
You can stay as long as you like.