I Think My Old Dog Died!

About a year ago I had this lovely dog named Sadie. Sadie was no older than 5 years old, she was a great pyrenees who I rescued from an abusive owner. Sadie would sleep with me every night we went on walks every day and I even trained her with her basic commands. Sadie was the best dog I have had but sadly I had to give her up. She became too much of a big responsibility and I know that sounds funny because great pyeranes are a huge responsibility but at the time of having her I lived in a small 2 bed apt. I was going to school and working and having to come home to a big dog that needs to go out on a walk every day just made me feel more exhausted. So after having Sadie for about 6-8 months I took her to a dog shelter that takes dogs and doesn't kill them after a couple of days. I felt so bad for doing this because I didn't know who she would go home with. I cried the whole way home. The next day I get on the website and check to see if I could see her on there and I did find her. The website takes down the dog after they get rid of them but sometimes when they are behind the website will say that the dog has been adopted already. Well I get on one day and I can't find her at all. I call the shelter asking if they got rid of a great pyrenees and the guy I spoke to would not tell me. I was so heart broken because I wanted to get Sadie back but I just could not take care of her the way she needed to be. So, about a year has passed and as I was going to bed I start to feel all this pain and sadness and the first thing I think of was Sadie. I start to cry because at that moment I knew she had died. I was so upset and angry with myself for not doing better with this dog. Sadie is the only thing that I can say when asked if I've every been in love. Have any of you loved a person or pet so much that you lost contact with but know when they have died? If so how did you deal with it?