Most Helpful Guy
He probably thought he was okay with it untill he saw you actually going through with it and now it's actually sinking in.
So he's realized that he does not want you to change your body like that. I don't know if you could convince him otherwise, few men want fake breasts.
Most Helpful Girl
I think it's best to first discuss with him WHY he changed his mind. Ask him what changed between the time of you expressing a desire for the implants to actually making appointments. Maybe he's scared that something might go wrong, maybe he prefers the look/feel of your natural breasts, maybe there's another issue. What I'm saying is, try discussing and figuring out his exact reasons. Then, go from there.
If he ends up not knowing why he doesn't like it, then he really doesn't have much ground to say yes or no to your implants. However, if he has valid reasons, you guys can both discuss your pros and cons, and take things from there.
Ultimately, it's your body and if it's your desire to get implants, then it's not really his place to say no. Plus, if implants have the power to cause serious problems in your relationship, it might be time to re-evaluate even being in the relationship at all. Best of luck!