Long-lasting or enduring; often used to express the wish that a relationship, happiness, or prosperity will continue for many years.
ご結婚おめでとうございます。末永くお幸せに。
Congratulations on your marriage. Wishing you lasting happiness.
末永いご支援とご愛顧を賜りますようお願い申し上げます。
We humbly ask for your continued support and patronage for many years to come.
二人が末永く友人でいられることを願っている。
I hope the two of them remain friends for a long time.