I've been with my partner for 7 years, not married, and dd has his surname. It's never been an issue. This might be strange but I like that by name she 'belongs' to him. A bit silly but everyone knows she's mine, but I like her name tying her to him. But like lili81 said I think it's just a name and doesn't define who she is.
Also if we ever got married I wouldn't change my name for professional reasons.
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