I gave away my dog. I am now extremely sad.?

I gave my dog away 2 days ago to my boyfriends half brother. She was a 6 year old Chihuahua that I had got off of craigslist around 1 year ago. I got her from a couple who locked her in a bathroom most of the day while they worked. She was the sweetest most beautiful dog ever. The problem is that I never spent that much time with her which I deeply regret. My mom worked so she was not able to spend any time with her and sometimes I was not home for days because I would be at my boyfriends house. When I was home I still didn’t give her the attention she deserved. All she wanted was love and attention and even though I loved her very much I didn’t show it that much. I have another dog who is also a chihuahua and I wanted a playmate for him but having 2 dogs was becoming difficult to handle. Not to mention I am pregnant. I need to be able to focus a lot of my attention to my baby when he comes so I felt that giving her away was the best I could do. I can’t help but to feel like I made the wrong decision. I wanted my dog to be happy its just I always thought she would be happy with me, I feel like I betrayed her. I know where she is and I know she is with so It makes me feel a little better but I still can’t help but to want her with me. I told my boyfriends brother that if for some reason having her did not work out then he can return her back to me which if he did I would not give her away again but I know that won’t happen. I just feel regret for not being there more for her. I know that I helped give her a better life but I miss her dearly. When my boyfriend gave her to his brother I cried hysterically. I felt as if I was losing my child. At the same time I just hope I did the right thing and that she is happier. Have any of you felt this way after giving up your pet? How long did it take you to get over it and how did you?