Who Should Get The Cat?

My old roommate, Elin, formerly owned a cat (which I also used to live with) named 'Papa'. About two years ago I moved out of our apartment, she kept the cat, and I moved into an apartment with my boyfriend (Paul) and our mutual friend (Emily). A little over a year ago, Elin was forced by her new roommates to give up 'Papa'. She came to us, asking if we wanted to take him, saying that if not, she'd have to find another home for him. We took him gladly and have been his caretakers since that time. Emily, my roommate, has since taken over the majority of the caregiving for 'Papa', cleaning his box, buying him toys, providing food, etc. Paul and I have helped, too (mostly on a monetary level -- and with love), but she's really been his primary caretaker for a little over a year now. Elin has been by our apartment dozens of times for social visits ('Papa' never being the primary reason for the visit) and has not provided funds for food, litter, or anything during this time. It's also important to note that at the time we took 'Papa', there was no paperwork involved and no expectations put on the situation that Elin would ever take 'Papa' back... This is where it gets tricky. Paul and I are now breaking up and I'm moving out of our apartment. During the last year, Emily has created a real bond with 'Papa' and does not want to give him up. I'm not in a position to take him with me to my new apartment and would rather he stayed with someone who REALLY wanted him anyway. Since Elin has caught wind of this, she has made it known that she wants 'Papa' back. Unfortunately, Emily is now unwilling to part with him. My question is...what legal claim do either of them have to ownership of the cat? In my mind it's pretty cut and dry that Emily is his owner and should maintain ownership status beyond this current situation, but as there are friendships and high emotions on the line, I'm wondering what side the law would actually fall on?