Fiancee and my last name...?

So, my fiancee still has her ex husbands last name, and the only reason she has it, is because she has a son, and she wants to have the same last name as him. I understand that, and i totally respect that, and shes decided to hyphenate his name, with my name when we get married. I dont know how i feel about that. I mean, most of me completely understands that she wants to have the same last name as her son, but theres a little part of me that feels upset about it. I mean, i dont want my name hyphenated with his. Sometimes when i think about it, and it upsets me, i feel selfish, but, i donno how else to feel. In every aspect of her life, she puts her son first, which i totally get and respect, and truthfully, would hope she would...but, i donno, i just wish for one time, she would put me first and drop her ex husbands last name. Im caught in such a catch 22 because, on the one hand, i want her to be happy, and if keeping his last name to match hers with her son makes her happy its what i want...but on the other hand, i kinda feel like its a slap in the face. I just want to be good enough for her that she would take my last name only. I donno what to think or feel. I dont wanna come across as selfish...but, its how i feel. Taking my last name means so much to me..i would feel so honored if she took it, and dropped her exs last name. But i also know, understand, and respect her reason for not doing so. If theres anyone out there who can shed light on my situation, or give me some advice, or ways to look at this differently, please...chime in.