We had to put my cat down this morning...?

she was only 14 years old and I've had her pretty much my entire life. We found her in our yard when I was 4. She was my first pet. She was sick for about a week and we took her to the vet and they found out her liver and kidneys were bad. There was nothing the vets could do, so we had them put her down this morning. I'm so sad and I can't see myself feeling any better anytime soon. I can't stop crying and I just want to hold her one more time. I keep looking around where she used to lay and wishing she was still there, all cuddled up on her favorite stool. I didn't even get to say goodbye to her. I just don't know what to do because my dad thinks I'm overreacting and that I should be over it already. But it just happened this morning! How can I already be over it?! We had plans to go over to my aunts house this evening, but with all that's happened I wasn't up for it and he got so upset with me. But I can't help the way I feel....I just wanted to be alone and to mourn...Does he have a right to be angry with me!? I don't think he does....