I'm so sorry. I know I'd be thinking these same thoughts, but you know what? It's all working out the best for everyone, considering. I don't think you're a bad person for not KNOWINGLY choosing a child with potential problems. I do think it's different than having a bio child with problems. You are not a horrible person. You just know your limitations. You can't compare yourself with others. Do you think people who don't adopt are horrible? Yet you are willing to give a good home to a child when many others aren't. It just isn't their path while to you, adoption isn't a sacrifice, it's a joy. Do you think the birthmother is horrible for giving her child up for adoption? No, it just wasn't her time to parent, and her situation has now made another couple very happy. I just don't think comparing yourself to others or some ideal will do much except make you miserable and second guess yourself. Littles is now going to have a loving home, and you will move on to the child that is meant to be yours. Meanwhile, you are now in a position to help other people who may encounter this same situation some day. You have acquired the gift of comfort and wise counsel for some other couple beating themselves up. I know it came at a high price and may not have been something you wanted, but that is something positive to take away from this.
Take time to be sad, but after a bit, take a mental break, do something that makes you happy and once again start to focus on the baby that WILL be yours.
Hugs to you!!!!!