If he wants to throw a relationship away because your boobs aren't natural, then let him. There are likely other issues in the relationship that you may have overlooked or ignored, so in a way he's giving you a gift: the freedom to find someone more mature and reasonable.
I think your girlfriend is being naive here for sure. But it sounds like she has good intentions and thought that he had good intentions as well, she's just guilty of being a bit sheltered. So what is it that you're upset about and ideally how would you like the situation to be resolved?
If he wants to throw a relationship away because your boobs aren't natural, then let him. There are likely other issues in the relationship that you may have overlooked or ignored, so in a way he's giving you a gift: the freedom to find someone more mature and reasonable.
This is not about trust
Can I ask what it is about?
I think your girlfriend is being naive here for sure. But it sounds like she has good intentions and thought that he had good intentions as well, she's just guilty of being a bit sheltered. So what is it that you're upset about and ideally how would you like the situation to be resolved?