I think you're overthinking things. I don't read any worrisome danger signs, but I can tell you that as a male, we always have a massive initial surge of enthusiasm for something in the beginning, and talk about it a lot at first. Then it gets put on the 'to-do' list, and we tend to focus on more pressing matters. Even something as big as a marriage is definitely something he'd want his space for. I suggest leaving the subject for a while, then doing a bit of your own planning, telling him you want to run it by him to get his input, etc. etc. Keep the subject alive, but don't bring it up consistently.

I can say with considerable certainty that I doubt you've got anything at all to be worried about. If the marriage doesn't happen this year, it'll be even better next year. You can still look forward to it, and in the meantime, he's not going anywhere.