Difficult at this time of year - this is caused by too much water, irregular watering, or a lot of water after not very much, but also, temperature fluctuation, link below, you'll need to copy and paste into your browser

https://www.rhs.org.uk/advice/profile?PID=393

You are over watering your tomatoes and that's why they split. Too much water also ruins the flavor, creating a watery bland tasting tomato. It also leaches away vital nutrients from the tomato. Keep the soil on the dry side, just barely moist.