Big fish narrows the list somewhat to: Belize
Also there's a lot of mainland activities to do outside of Belize City the 2nd week. Maybe stay at/near Dangriga (Hamanasi, Inn at Roberts Grove etc.) and you can dive mornings and tour the Mayan pyramids, jungle treks, jaguar preserve, howler monkeys, cave tubing, ziplines, river tours, Belize zoo, (tell me when to stop...)
If you do the Pearl it runs between Utila and Roatan. I've spent a week diving both. The Whale Sharks would be gone from Utila by June and the only other sharks we saw were occasionally on the north side. Like maybe every 3rd dive. One site on the south - Black Hills had bigger stuff, Oceanic Triggers, Cuda, Grouper etc. When the Pearl was the Utila Aggressor she was moored near there one day. On Roatan about the only sharks are at the Shark Dive - IDK if the Pearl stops there - it's done thru Waihuka Shark Dives. We dove the north side for a week and only saw turtles and a few grouper. The Dolphins are at Anthony's Key - IDK if the Pearl stops there either. She did moor one day out east of the town of West End so they may have that option. Sometimes dolphins are seen in the wild off SE Roatan also.
Roatan would be about the only nearby option for the 2nd week on shore - Utila is really small and quiet, not a lot of great beaches either - most of the island doesn't even have roads yet. Your husband would be bored the 2nd day. Roatan has the beaches (West Bay) diving, ziplines and a few local attractions but not much else IMO. If I wasn't diving I couldn't spend a week on either. You could dive, it's pretty cheap there. $30/boat dive in the West End for 10 or more. But you'd likely be looking for something to do most afternoons. You don't want Mainland Honduras, it's currently the murder capital of the world.
The other thing you may want to look at is flights. I believe you have to be in San Pedro Sula or Roatan early afternoon to catch the (extra cost) Utila charter flight to the boat. At least that's how it was when it was an Aggressor. There's no lights at the Utila Airport so it's all day flights. People have mentioned if you have to overnight in SPS to pick a nice hotel and stay inside...
I haven't done Saba/St. Kitts but when we considered it a few years ago trip reports I saw indicated it was mostly small stuff.
If you do the Saba/St Kitts return trip (ending in Saba/St. Maartin) -
I think you can get to several other countries pretty easily thru San Juan, PR. I know it's possible to go from St. Maartin thru San Juan to St. Thomas in about 2 hours. Around $400 U.S. That would open up St. Thomas, St. John, St Croix, and Tortola or Virgin Gorda in the BVI's - all are within 1-2 hrs. of each other via the fast ferries. The BVI's in particular have stunning, isolated beaches. All the islands also have good diving and other things to do - Virgin Gorda is a little quiet. The Baths there are a good snorkel.
Antigua, Barbuda, Dominica, St. Lucia - all might be possible thru San Juan also - based on what I saw leaving the American Eagle terminal while waiting for a local flight a few years ago.
I think you can also get to Anguilla from the north side of St. Maarten so if you visited both the French and Dutch sides of St. Maarten first, there's three countries to tour. Anguilla is pretty small...
Could your husband find enough to do on Provo? - Turks and Caicos.
Beautiful by Nature - Turks and Caicos Islands - there's some nightlife, fishing, at least one casino. For you, Grace Bay Beach is one of the finest in the world.
Either the Aggressor or the Explorer are big fish trips. Here's an example:
Saudio's Trip Reports - thanks to Mike Southard for this. We saw the same stuff 2 years ago minus the dolphins - plus dozens of rays. Kind of pricey to stay on Provo though.
On the land-based option - if you're talking 2 weeks, I wouldn't go to Bonaire. There's not even a lot of great beaches for you. Consider Curacao instead - same shore diving as Bonaire with much more to do. Also unlike Bonaire most of the shore dives are also just off pretty nice beaches. There's more people there so many more restaurants, about a dozen casinos, some nightlife etc. Bonaire can be pretty quiet...
It's also about $60 r/t mid-week to fly between them if you wanted to change islands for a week. Depending on connections, there's a chance your flight to Bonaire will first stop on Curacao anyway.