Want another baby

My boyfriend and I have a 5 month old and before we had her I really wanted a baby and he always told me "maybe we can have 1" but it was always an argument because i always said I have to have more than 1 baby. Well we got pregnant, pretty much on purpose (for the both of us) since we didn't use any form of protection at all and he has always been happy since the moment we found out and he loves our daughter to death. But now when I bring up having another he still says no more and it really is killing me because i know I'm supposed to be a mom to more than one and would hate to not give my daughter siblings. He always says he's going to get a vasectomy and I can't tell if he's kidding but I told him I'm not getting married to him if he does that and since he doesn't want more because I'm not going to be fully tied down to someone who doesn't want the same as me and he acts like he's okay with that. I can't tell if he's just saying all this because be feels that he needs to stick to what he's always said since he hates to be "wrong" and everyone keeps telling me he will change his mind. But I can't stop thinking about it. I don't want another yet, but I really do sooner than later. And I get so jealous seeing pregnant women even though I was literally just pregnant😒 Has anyone else's boyfriend/husband said the same and then changed their mind?