After you've lost someone, you may feel guilty. You may be preoccupied by thoughts like, "I wish I'd said goodbye one last time," or "I wish I'd treated this person better." Don't allow yourself to be consumed by your sense of guilt. You cannot change the past by mulling over it again and again. It's not your fault that you lost someone you loved. Rather than dwelling on what you could have done or should have done, focus on what you can do - process your emotions and move forward.
If you feel guilty following a loss, talk to other people who knew the person or pet. They will almost always be able to help you convince yourself that the loss isn't your fault.