I am willing to accompany your entire life 这是最标准的翻译。
I will stay with you forever and ever.
ps:will表示坚定语气,说明决心很大;forever and ever比forever更深一层,起强调作用。
I am willing to accompany you my lifetime.
希望对你有帮助
I want to be with you forever.
I would like to be with you all my life.