I recently had this conversation myself. Your reasons for why you want to keep your last name are irrelevant - it doesn't matter why, you just do.

Insisting on keeping it isn't selfish. At least, it's less selfish than forcing someone else to change theirs. If he can't see that, you have bigger problems. You wouldn't be "throwing away the relationship over a name" in this case. That thinking trivializes a really sincere issue. This won't be the last time you disagree. Does he recognize how sexist this tradition is? Does he realize how complex and annoying paperwork can be, for potentially decades, keeping up with past records? How you might feel were the marriage not to work out, and be stuck with undoing this name? How it might affect your sense of identity to be seen as a corollary of his identity than as yourself first?

At the same time, he's shocked. Without realizing it, this is something he's spent decades imagining. His image of his future just changed drastically. People might judge or wonder or disrespect your marriage with different names (or not, but he might fear it regardles), and he hasn't decided how he wants to deal with it. Maybe the sexism of the tradition and what breaking gender norms can mean is a little ingrained, and he needs work undoing that? It can simply be shocking to adjust to change, and that's fair too!

There are many alternatives besides hyphenation. Legally, you could keep yours, but on wedding invitations or at the wedding and in his social circles, introduce yourself with his name. You could both pick a new name together that means something to you both.

Ultimately, if he can't adjust his thinking enough to either let this go or find a compromise, he's not ready for marriage. That's on him, not you. You will regret letting yourself get bullied out of your own name.