Hi There,
It is so hard. Im sorry this is happening to you, I want to let you know that what you feel is valid and important.

I have a little story to tell. I have a relative who is 25 and last year fell pregnant to someone she just met and is not in a relationship with him. He lives overseas and is married and has other children.Its not an ideal situation for her to have a baby in- but she is doing it. I am not judging her.
Her immediate family are housing her and she had a healthy son. I wish good things for her and her son.
I have not seen her or met her son.Last week she invited me to her sons Christening. I am not going- I cant go, I cant be involved. I need to maintain my own space around myself. I am not hiding or anything but it hurts me too much. I suppose what i am trying to say is one of the hardest things to overcome is that other people are doing their own lives- and that we cant ask them to change that, can we?
Even though it hurts and it seems all wrong. I understand that you want to keep from your sister how much it has effected you. Dont forget though that your sister cares about you and is probably aware of how this could effect you.
xx best best best
and like Lisa said cry as long as you need to...