I've lost a lot of weight over the past couple of years with a lot of work on diet and nutrition and exercise. In general, diet and nutrition are more important than exercise and the type of exercise can make a big difference.
For diet, I cut out as much sugar as I could (I typically eat under 20 grams per day), dropped carbs to 20-33% and track everything that I eat using the Livestrong MyPlate web application.
On exercise, I recommend "The hierarchy of fat loss" by Cosgrove. It's reproduced all over the web but here's one link. If you were in the Boston area, I'd suggest going to one of Mike Boyles fitness places to lose the weight but you're not in this area.
Tennis is what I'd consider a great interval workout and you can lose a lot of weight playing tennis but you have to be fit enough to move and moving around the tennis court puts a lot of stress on your lower joints. I would look into doing interval workouts that don't put a lot of stress on your joints and keep the tennis light. That joint stress can haunt you when you're older.
Are you still on the antipsychotics?
I have a series of pictures from really fat to where I am now and most people can't believe the pictures - I keep it on my phone.