Jo,
Sweet
Don't be so hard on yourself you need time to grieve for the twin. It does not mean you are not grateful for what you have. I am sure you will be a great Mum belive me there is a friend of mine who has not lost a twin and she still gets frustrated at those who fall so easily and take thier kids for granted. I would say it shows more about how much you love cherise and want your little bundle.
Hang in there I am thinking of you