I have a similar situation. I was in a relationship at the time I booked the cruise but as you know, nothing lasts forever. as such i will be cruising alone. I am going follow the advice that I have seen on these boards and play dumb because repricing my cruise would not be pretty as I booked a suite for the first time. I am not too worried about a refund though it would be nice (as I paid for the entire cruise) I just don't want them to charge me anything extra as this cruise is already expensive enough.
nothing too ground breaking on my end. i wear my trusty adidas track outfit with one of those snarky walmart t-shirts. make it through the terminal. find someplace to eat and grab an adult beverage (I think this year I will aim for pig and anchor. i heard it is open on embarkation day). wander around and people watch ( no shades. because i lose or break them). send pictures of ship to the family (to make them jealous) as I wait for the rooms to open. once I am in the room do the whole sanitizing thing and take pictures of the cabin (to make the family jealous again). then I finally change clothes and run to the gym real quick and get a workout before they close it for muster ( but that depends on the cruise line). if i remember my cruise on the Vista correctly the gym was closed until after the muster drill ( if that is the case i am sure I will find something else to do).