Why is this dog acting this way?

I bought my ex a chihuahua for her birthday but we ended up breaking up and I ended up keeping the dog. He is honestly so freaking stupid. He always whines and any time anyone pets him, he starts shaking and yelping, basically screaming his lungs out. He wont play with toys or act happy at all. He sheds like crazy but if I try to brush him or give him a bath, he starts screaming. He's always scared and when he's scared, he pees in my floor and will not stop until you go lock him up in his crate and cover it with a blanket. I try to treat the dog right but he is seriously getting on my nerves. I cannot take it anymore. What do I need to do?