106. "It would be easier if you were married to your S.O." In response to In response to 0
Assuming you two are not married, but...
If you really feel uncomfortable being called dad by your S.O.'s 8year old, then why not sit down with the child and explain to the child why you preferred to be called by your name?
As for your S.O., she should be understanding and supportive of your feelings on the matter. I understand that people do not want to disappoint children, but children can learn to accept certain disappointments if explained to them in a way in which they can understand.
If I was in a similar situation, then I would not want to be called dad unless said child(ren) were infants and I helped raised them to the age that they are. Even then, I would let them decide whether to address me as dad or by my first name. I think what is more important is that they respect me as the man of the house as well as know that I love them like they were my own bio children.