To find out or not to find out, that's the question

I know there must be thousands of threads on this subject by now, but I’m really struggling to decide…

When I was pregnant with Hjörtur, my first, I decided I didn’t want to find out the gender. My now ex husband was set on finding out though. For him it wasn’t an option that only one of us would find out, it was both or neither. So I gave in and we found out we were having a boy. Somehow it just didn’t feel right for me, but of course there was no way of undoing it.
After that I said that if I’d ever have another baby, I definitely wouldn’t find out.

Now I’m pregnant with my second child, my new SO’s first, and we agreed on not finding out before we even properly started TTC. He said he wanted it to be a surprise. Also, we tend to keep things like outfits, the nursery etc. as gender neutral as possible (as I did with Hjörtur). I’m now almost 13 weeks pregnant, we had the blood test weeks ago, and the gyn knows the gender of our baby, but we told him we didn’t want to know. But ever since, SO has doubted his decision, and now told me he wants to know. At first we agreed that he’d wait until the echo at 20 weeks, but he doesn’t want to wait that long. So now we’re thinking that maybe he could find out (by asking our gyn), and not telling me. Has anyone done this, one parent finding out without telling the other? Is it even possible, going an entire pregnancy without telling the other parent “by accident”? Or maybe I should find out as well anyway?
SO has said that if I really don’t want him to find out, he won’t, but I don’t think that’s for me to decide.