My current situation is this...I have been divorced for 2 years now. I have one daughter and my ex and I currently have shared parenting where I have her 60% of the time. My daughter and I have a great relationship, and I would even categorize my relationship with her father as productively functional. The problem is, I am having a hard time letting my daughter go when it is time for her to go to her father's. I literally still cry and sink into this depressed state in which I feel like a horrible parent. It's not right that a mother is without her child for 3 days a week, and even though I know this is how it has to be, I am not dealing well with it at all. I don't know if I ever will.
No matter how hard this is, your child is yours and his and a child can only benefit from having a relationship with BOTH parents. Obviously this is fairly new to you, and I know from my own experience that your child during upsets and drams become so important to you, and fill a void. So when the child is gone, you are alone and faced with your own worries and fears for there is nothing else to focus on.
This is where you should be taking the time for yourself. To grow and learn and meet new people. Make plans for YOU on the days that the child is gone. The child is not with a monster, he or she is with their dad, who loves him or her just as much as you do.
You are not a bad parent for doing this, you are good and fair parent and putting your child's needs first. Think of it that way.
It is all a process and something that you have to get use to and you will. Give it some time.