No more kids

Me and my SO supposed to get married soon we have one son who is not even one. My SO wants more kids he said maybe not right off but he definitely want more. Now we are arguing because i don't. I never really wanted kids and always said if I had one it will only be one. I hated being pregnant and God knows I miss sleep and just regular life in general while his life haven't changed much. He told me he not sure we should get married because he always pictured hisself having at least 3 kids. I think its good i gave him 1 considering I didn't really want any. He have this thing about our son having a sibling because he didn't have any. I told him i had 2 you didn't miss anything but he is really admit aboug more kids.