When we get married, I'd like to share my last name with my girlfriend.
OK, why do you want to share names?
I think it can be a symbol that we're a uniform couple.
Normally women adopt their husbands last name. You should talk about this before you get married so you can be on the same page as her.
I love her so much and she is going to be the only wife I will ever have.
That's great! And if she agrees with you about the name sharing, that's also great! However, you really should has this stuff out before the wedding, because being open and honest with each other provides a strong marriage in the long run.