Hi Sunlover! (Nice handle, by the way!)
Don't worry, your english is great. I've heard mixed reviews about SAI, and since I've never been myself, I can only tell you what I've heard and researched. San Luis is the property where the beach is across the street from your hotel, however the good news is, it's said to be one of the best beaches on the Island. San Andres is commonly referred to as the "little Jamaica"... a mix of Latino and African roots can only mean one heck of a great party place! I do not know about specific places for nightlife off the resort, but I do know of a forum that will be able to answer such questions:
Another link you will probably like to check out that will give you some good information about the hotel services and activities as well as some pictures:
As you can see, San Andres is on my wish list! ;D
Make sure you contact me when you return, but I'll PM my email address to you in the meantime.