My dog just died, how do I cope?

I knew this day was coming for a while now. I got my her when she was around 2 or 3 while I was in kindergarten. I am now about to come up on my 20th birthday. We booked her an appt about 2 weeks ago to have her evaluated, but since then she stopped eating and drinking. When we drove to the vet today I held her in my lap. I miss her so much already, but I feel so angry. Not angry because she died, but angry because for some reason, my sister’s husband came with us. I do not like this man, I haven’t since I met him when I was 12. I know it sounds selfish, but his presence and him trying to not have me look although I chose to stay in the room with her,pissed me off. I was trying to watch my dog peacefully die because I felt like i had to and I know i wanted to. I did not need to hear him or him telling me what to do…. I guess I got a little off, but how can I cope when I am so angry that I was robbed of being peacefully with my dog as she died? I am angry and I am also frustrated with myself that I let him bother me. I don’t know how to feel.