Yep. I also felt like I had betrayed Scottie when I brought home Casie. Scottie was
very upset with me. It took Scottie maybe a month to accept the fact that she was not leaving, another month to be comfortable around and near her, and then another couple months to want to play with her. It was a very slow transition! My dreams of wanting two fur babies to cuddle and spoon each other while sleeping went flying out the door!
It's been about one year now. I can't say they absolutely love each other, but they definitely enjoy each other's company and play together lots!
With time, they will bond. Don't worry!