Cream cheese has a high water content so it's more likely to split than regular buttercream. Usually, it splits due to a temperature issue. Your ingredients may have been too warm or cold or you're environment is too warm/humid or cold. If you haven't already added the sugar, don't worry. Just mix in the sugar and it'll help everything come together. If you've added the sugar and your frosting has split, you'll need to heat or cool the frosting (depending on the initial problem). I'd recommend either: 1. Heating up the bottom of the bowl with a hairdryer or placing it over a saucepan of boiling water (like a double-boiler). 2. Chilling the frosting by popping it in the fridge. Then beat the frosting again! You can also add a little corn starch which helps absorb the extra liquid.