Hi Bev
Sorry to hear about you situation ,you do not say how old your father is or how old you are??.
It must be hard on you,but if your dad chooses not to tell you,there is no way you can find out!!!!
You could approach the situation by saying you have been on the Myeloma UK site,because some one you know has Myeloma and you found it very helpful and useful,if your dad has myeloma he just might ask about the site,you are not actually being untruthful,he just might help him to open up.
They might feel they do not want to worry you,or by denying it,might be a way of coping,our family know but we do not go into everything with them because we have to have some normality ,.hope this helps Eve