Living in Belize for four years, I would suggest that u add some land tours to your itinerary. Belize is famous for its eco-tourism. Western part of Belize is covered with tropical rain forest. The view is fantastic. You may want to take a day trip to Tikal, Guatemala. Its a famous Mayan archeological site. There are local tour operators who cater to visitors.
If you are looking for night life, you may want to stay in San Pedro instead. Placencia is a quiet and small town. You are not likely to see many people there. Belize has the world's second largest coral reef, there are numerous diving sites along the coast.
Belize is very hostile towards homosexuals. I don't believe there is a gay venue in Belize. Also, you have to watch-out for robbery. Do not walk alone at night, or during the day in remote areas.
I hope you enjoy your time in Belize.