Check out travel websites and look into the Hedonism resort packages. Here you can find a list of various all-inclusive resorts that are exclusively for people 18 and older.
Choose an theme for the vacation, as this will ultimately determine the resort you choose. Adults-only resorts can range from relaxing spa atmospheres to romantic to fun that's a bit on the wilder side. By the way, that usually means lots of nudity and yes, sex between two or more people out in the open.
Research Jamaican attractions to find those with adult atmosphere and accommodations. Find out about the nightlife and club scene. Remember, some resorts and clubs are adult-only and all it means is no kids are allowed. There are also adult-only clubs that are clothing optional and pretty much anything goes. Make sure you know what you're getting yourself into early.
Keep clear of cruise vacations, as it is quite tricky to find any that are adults-only. While many cruise ships do offer special entertainment just for adults, their ultimate goal is fun for the whole family.
Consider renting a timeshare instead of going the resort route. This may be a bit more expensive, as most entertainment and activity will come out of pocket. However, if you are in the market for a quiet, private vacation, this may just be the right avenue for you.