We were in St. Croix quite some time ago (2009) and we were warned about theft directed at tourists at that time. In fact the cruise ships had stopped coming to St. Croix because of the crime problem. We spent a week on a liveaboard and then a week at a land-based resort. We rented a car and drove all over the island. We found the people were friendly and we never felt unsafe; but we did heed the warnings and we never "strayed very far off the beaten path". Since then the cruise ships have returned to St. Croix and I have heard that things are much safer, but I don't have any personal knowledge. But I would go back to St. Croix.
Regarding the 2 places you've suggested, Belize and St. Croix, we've also spent a week on a liveaboard in Belize and a week at a land-based resort on Ambergris Caye (and a few days in Belize City) and we felt very safe in Ambergris Caye.
Of the 2 destinations, I think the diving in Belize was better but they were both nice and the Fredricksted Pier in St. Croix is one of the easiest and best shore dives that I have ever done. Really fantastic with seahorses and frogfish and octopus and loads of other critters. But you can't dive the pier when cruise ships are in port.
The reason we haven't gone back to Belize is the mosquitoes. I probably sound like a wimp but I am very sensitive to mosquito bites and I get big, itchy, red welts that persist. I don't know if it was just our bad luck but the mosquitoes on Ambergris Caye were the worst I have ever encountered. We also did a land excursion from Belize City and I got badly bitten then too. Of course it was fine when we were on the liveaboard boat.
Maybe there just wasn't any breeze or something when we were on Ambergris Caye, but you had to wear mosquito repellent just to walk a few doors at night to a restaurant, and you still got eaten alive - and forget about having dinner outside! I remember one night when the entire island lost power for several hours, it was swelteringly hot in our hotel room but we didn't dare open the windows or doors because of the mosquitoes. My husband is usually not bothered very much by them but even he thought that they were really bad.
Our experience may not have been typical, and of course it is no surprise that one encounters biting insects in the tropics, but every time I think about going back to Belize I remember the stings and itches and change my mind. We had to take Malaria medication when we went to Belize and now that they have had quite a few cases of mosquito-borne Chikungunya and Dengue Fever, I am even less enthusiastic about returning to Belize - they don't call that area the "Mosquito Coast" for fun! But I don't know if the mosquito-abatement programs have improved in recent years, you should talk to others that have been there more recently.
As far as your husband wanting to see something different, I would suggest Little Cayman or a liveaboard to the Turks and Caicos (sharks and rays on just about every dive.) But the water is kind of cold in those areas during February (low to mid 70s) so you might want to go someplace further south for warmer water.
Diving off Kona in Hawaii is also different and great, but again the water would be rather cold (IMO) in February. Good luck finding a great destination!
