Your brother or sister may turn out to be your best friend someday. Many siblings fight and compete with each other while growing up but become very close when they get older. As you grow up, your friends might change, but your family is yours forever.
If your pet has died, try not to obsess over “When am I going to get over this?”. Instead, focus on small steps in your adjustment process: put away the leash; be able to pass the park without getting upset; and, eventually, feel the urge to get a new one.
Write down everything that is good and positive. Are you thankful for a loving mother? A supportive father? Even something like having a roof over your head counts. Write it all down and reflect upon it. Practising gratitude can give you perspective.