How far is attachment allowed?

My dog has run away and I am sad. To be honest I was probably not taking care of him the best as one possibly could. We both excelled or declined based on my success, but I tried to allow him his own freedom and now he is gone. Do I grieve? I mean I know that I am but should I? Is this precisely the type of attachment I should and must choose to sever? This dog has been my friend and cohort for almost 10 years. He helped me recover from heart attacks and multiple surgeries. How could one not grow attached? So should I feel relieved or guilty and sad? I made sure to ask this while he was missing. Now he has since been found and returned.