I know it is easer said than done, but try not to be hard on yourself. It takes courage to decide what you can handle and what is in the best interest of the baby and act of that decision. The baby will be with a loving family who knows that they can handle the challenges that they may face ahead. You were there to care for him and love him and ensure that he got to his family.
I made the difficult decision to end a pregnancy when I found out that the baby had downs syndrom. Many people would not have made the choise that my DH and I made but we sat down and discussed this even before having the amnio. We felt that this was not something that we could handle. I beat myself up for a long time especially when I started down the IF road. I felt that I was being punished for my actions and as a result would never have a child. Those nagging thoughts returned when our first adoption was disrupted. I believe that DH and I made the right decision for us and our family and no longer feel that I was being punished. Thre kids and millions of diaper changes later, I know that we have the children that were meant for us.
So... try not to listen to any negative things that anyone else has to say and most importantly do not be down on yourself.