Just tell him you're not comfortable adopting names like dad and poppy yet - his first name will do for now. It takes time for bonds to grow.

I have a wonderful stepmum and I refer to her as my stepmum but I *still* call her by her first name..."mum" just doesn't feel right. This is 25 years in and i love her to bits and it doesn't change the way I feel about her at all. Just do what seems right to YOU, there aren't any 'rules' that apply in situations like this.