So back in August, I lost my best friend and my little Spark - MOO

he was my 15month old kitten - who we rescued from being dumped out in the rain!
He had the best personality and pulled me out of a rough patch in my life.
He was my hot water bottle, my cure for tears and my spark within me and he truly was my best friend.
Moo was a lovable kitten and always showed affection to everyone who met him - all except one! my crazy ex-house mate.
She was only there a little while, but when she clashed with my other house mate i guess I copped the raw end of the deal and the way she knew she could get back at us was to hurt the one thing i cared about most in the world.
We were in the middle of moving out and the crazy house mate had come home to collect her things and I had seen MOO that morning, bubbly and bright as he usually was, when i came home at midday, it was a different story.
I won't go into what i saw when i walked in the door but we rushed him to the vet, we thought it may have been a UTI but i was soon to discover it was worse than i thought.
I said goodbye to him at the vets that night thinking i would see him the next day, he was crying for me but i gave him cuddles and let him be.
THAT was the last time I ever saw my little man alive again. The next morning i received the phone call and my world came crashing down around me.
We were told MOO bled out internally due to a forceful blow to his stomach.
When i confronted the crazy housemate she confirmed she had kicked MOO because he wouldnt move out of the way... which means my baby would have suffered.
I know people may not want to read the above but i really havent told my story and i want advice on how to let go of the anger i have towards her, the emptiness i feel without moo and how to move on.
MOO now sits next to me in his photo box, his ashes will always remain close - it will never be the same.
This makes me even more passionate to stop animal cruelty. The RSPCA are involved in the case but it seems to be dragging and i want justice - but the justice i want, wouldn't be classed as rational!
Can any one please offer me some advice