I am sorry for this unfortunate incident and an unfortunate decision. I believe you can't get your puppy back anymore. In reality we can't forget anything. We can only cope with them and endure them. Over time there is a chance that these thoughts won't distress us as much as they are now. You can enter into Psychotherapy for your depression and anxiety issues and also to better develop your personality and have a better line of thought so that you won't repeat your patterns again and be more happy. Regards