not contacting for a while, a long silence

not contact for a while

long absence, (honorific greeting) for when having not written or contacted one for a while

I'm sincerely sorry; please forgive me.

apologetic / sorry / regretful / contrite

(honorific) apology, excuse

washing away sand to obtain something desirable, such as gold dust or rice / by extension, a fine-grained or careful sorting out or selection of something or someone

to wash away sand to obtain something desirable, such as gold dust or rice / by extension, to carefully sort out or select something or someone

long / (time) long, lengthy

chief, head, leader