It wasn’t clear if the OP already has children or not, but having an ultimatem is not the way to approach the disagreement!
I, too, thought that my children would sleep in their own beds. Co-sleeping was not something either my DH or I planned on. Our oldest, though, turned out to be a very needy baby. He nursed several times during the night and was very difficult to get to sleep. In order to preserve my sanity and try to get
some sleep during the night, we co-slept with him.
Being a nursing mom, I came to realize how much more sleep I could get if I didn’t have to get up and go to another room to nurse the baby. We now have our fourth little co-sleeper.
My DH doesn’t mind, and it is a really beautiful sight to get up in the morning and see my little girl snuggled right up to her daddy, safe and warm in his arms.
Since she’s 2 1/2 now, she starts the night in her own bed and will join us in the middle of the night if there is a bad dream, or first thing in the morning (because she wakes at the crack of dawn).
Anyway, I am so glad that DH and I were flexible about it before we had children. We had our own ideas, but circumstances forced us to open our minds and our hearts.