I started to interrupt the marriage proposal scene with an "oh shit" moment. Understand that this is My Favorite Crutch™, interrupting a conversation I'm done having but don't know how to end with some crisis or other. I do this all the time, to pretty good effect, and don't object to it in principle.
I do object to using this particular "oh shit" moment, because it's supposed to happen later in the story, dammit.
So, a different "oh shit" moment wouldn't go amiss here.