I was in this spot. I loved Declan but DH was just so so about it. I dropped it and explored other names, none that I loved as much. The day I went into labor, he just said he could not do Declan. I then suggested Nicholas, which I liked, but didn't LOOOOOVE and DH was on board with that. Now I love the name Nicholas and that is 100% what my son is (of course) and DH has come around to Declan a lot.
You can't push him into the name, but drop it for a bit, explore some other options, and don't expect to make any true, final decisions until later on in your pregnancy.