Oh, that is terrible! Whoever thinks you are nuts for crying for your beloved pet is a monster! It has nothing to do with being an adult, it has to do with the unconditional love and joy a pet brings to your life.
I will pray for you and for kitty and just know that soon you will start remembering all of the love and joy she brought you and you will be able to remember her with a smile.
Your grief is perfectly reasonable and you deal with it the way you need to. I lost my kitty five months ago and when I found this poem I made one out of cross stitch and hung it on the wall next to her picture. I hope it is a comfort to you as well:
Four Feet in Heaven
Your favorite chair is vacant now...
No eager purrs to greet me.
No softly padded paws to run
Ecstatically to meet me.
No coaxing rubs, no plaintive cry
Will say it's time for feeding.
I've put away your bowl, and all
The things you won't be needing;
But I will miss you little friend,
For I could never measure
The happiness you brought me,
The comfort and the pleasure.
And since God put you here to share
In earthly joy and sorrow;
I'm sure there'll be a place for you
In Heaven's bright tomorrow...
- Alice E. Chase