Meh-niversary 

meh·ni·ver·sa·ry meh-nuh-ver-suh-ree /me'nəvərs(ə)rē/
noun, plural meh·ni·ver·sa·ries

The celebration of the day you stopped caring about something that used to burden your spirit and live rent-free in your mind.

S: Guess what? Today, I was swiping on Bumble and I found MY EX on there!
R: Oh no, what happened next?
S: I swiped left and kept on swiping!
R: Yay! Happy Meh-niversary!

Meh-niversary by GilcoShmilco April 5, 2021

meniversary 

The monthly recurring date of a past event.

My girlfriend and I are celebrating our 8th meniversary this month.

meniversary by Mike3567243 May 28, 2008

Menniversary 

The day of celebration in monthly installments after a given event; an anniversary, but monthly instead of yearly

You mean your one-month menniversary, because 'anniversary' makes no sense when its less than a year.

Menniversary by twlhisdvkljh October 9, 2010