Maybe try talking to him about how he’s felt through all these changes? If he has a hard time relating to your new family and everything going on, perhaps he’s just worried that he’ll lose you. He could be holding on to the surname thing because he feels like if he lets go of that you’ll be gone in no time too?

Probably a bit of a stretch, but if he can’t express why exactly he doesn’t want you to change it, maybe there’s a deeper reason for it and he’s ashamed of it or something. I don’t know how much this surname stuff matters in America, but it doesn’t seem like it should matter that much as you’ll still be married and he knows you love him.

Also the whole hyphenated surname thing people are suggesting... sure, it’s a compromise but it doesn’t work for everyone. I have a double barreled surname myself and if I got married and added my boyfriends surname to mine it would sound absolutely ridiculous. Just because it’s a compromise doesn’t mean it’s the best solution ahah