My Shih Tzu

My shih tzu Heidi was like a child to me. Two years ago a former friend of my finance gave Heidi to me because he and his mother no longer wanted her and couldn't take care of her anymore. She was four months old and took to me quickly. I immediately fell in love with her. I went through a period of sever depression and Heidi kept me from delving into the depths of dispair. The former friend ended up scaming us and lying to us and being an all around awful person. After about two years of no contact, he started harassing us to get Heidi back in order to make us suffer. Despite my two years of care and love for Heidi and numerous medical bills due to an illness she had, the cops and this former friend showed up tonight and took my precious Heidi away. They said legally, despite that I took care of Heidi almost all her life, she is his property. He has had nothing to do with her for two years and the bills I've paid for her cost more than he spend on her to begin with. I not only lost my beloved dog but I will recieve no repayment for all of her medical cost. For all my love, care, and money I feel I have no legal rights to Heidi. I adore Heidi and I'm really heartbroken and I want her back so badly. I can't stop crying- she is like a child to me. How could such an injustice be done? What can I legally do? Please help me, I'm desperate.