I am sorry to hear about your mother's sister
This will probably be a hard time for you but it is good that you have nice people who will support you. Telling your best friend shouldn't be too hard beings she is your best friend :P Your boyfriend should definitely know sooner rather than later since it will be his child too and therefore his responsibility as much as yours. It is also probably best to tell your parents and anyone else that may need to know sooner to avoid the question of why you didn't tell them sooner. I hope everything goes well and works out for you
