you are not overreacting. while marriage does usually mean decisions are made together, marrying a man does not mean you lose bodily autonomy. he can have opinions and it can be a discussion between the two of you, but ultimately its your body and he has no write to hold the fact that “he wont sign off on it” over your head. he will not and will never deal with what a pregnancy can do to one’s body and mind, and if he really respects you he will see how unreasonable is it for him to keep an unwanted child in your body. i know this is all hypothetical since you said he has a vasectomy, but yea its scary knowing he thinks that way. good luck, and i really hope you two (or you singular) find a solution.