forever; everlastingly; for many years to come; ever
どうぞ末永くお幸せに！
May you both be happy for many years to come!
今後とも末永くよろしくお願いいたします。
I look forward to your continued support for many years to come.
これからも末永くお付き合いしていきましょう。
Let's keep up our relationship for many years to come.