Save Leo from FIP

Hi my name is Anna, & 1 year ago I found my kitten Leo in the alley behind my apartment building. He couldn't have been more than 8 weeks old - he fit in the palm of my hand. His tiny little meow saved him that night & I'm hoping to save him again. Leo was diagnosed with FIP a couple weeks back & I only just learned & gained access to medicine for him in the last couple of days. This medicine could save his life & I need to give my baby a fighting chance.
What makes Leo different from other cats? He would always respond when we talked to him. Always jumps up & lays on me, sometimes I would wake up to his tiny little body on my chest or shoulder. He is the friendliest cat, always checks out newcomers and lays on their lap. Jumps soooo high during play. I've never felt so connected to a cat before Leo & truly wish for him to live a long life years to come. Please help in any way you can. He's lost a lot of weight as you can see & barely eats, I'm afraid time is running out for him soon. 
Thank you.