It's such a tough rollercoaster of emotions. You couldn't predict how you were going to feel about your brother having a baby, and you also can't help those feelings. Have you spoken to your brother and his girlfriend about how you are feeling? I'm sure they would be very understanding considering what you are going through. Maybe when you speak to them you could ask them if you could come and see them and the baby with them quite aware that you may break down in tears. You might find that your reaction to the baby is different to what you expect. And even if you do break down, well your brother and his girlfriend would be prepared that it might happen, and it's not going to hurt the baby at all. It may even help you with the grief over your own situation.

Big hugs to you ♥