Sorry to hear about your cat. I understand that there are various issues which are contributing to the present emotional state. You will be beneficial by psychotherapy. Suffering is not the option. Ask for professional help by psychologist. After the detailed assessment by psychologist and psychiatrist one can take decision about medicines if needed. Sometimes it is difficult to accept the external changes but with the change in our perception and thoughts it becomes easy to deal with it without making much damage to self.

Hello Friend, Good that you are seeking a help. Looks like you are carrying some reservations about happiness. We can enjoy every moment of life if you understand the purpose and priorities in your life. Every life has a purpose and we realize it's potential only when we suffer or do some mistakes. You have an  opportunity now to explore yourself and figure out this. You first need to assess yourself first and identify the negativity which is causing stress or depression . Then you can work on the possible solutions to recover. But all these would need a assistance of a psychology counseling process.