I understand how you feel.
We had a couple book the exact same holiday as us earlier this year. I have posted about this previously. We had booked last summer for a holiday in February 2022. I purposely didn't tell them as we had been on holiday with them before and I prefer to go as a couple.
They found out we were going on holiday (without them
) and booked the exact same holiday - without asking if we minded.
I suppose Lizzy you are lucky that you are not going on the same dates.
On the one hand, you could agree not to see the couple until after you return from your cruise, so that it doesn't spoil your new experience. I imagine this would only be a couple of weeks.
On the other hand, as other posters have said, they might be able to give you some useful tips.
I don't think you ABU. It is hard not to discuss plans with friends. I want to book a holiday for later this year but haven't done it yet as I don't want to tell the other couple and I am not a very good liar.