I have had the same problem (once) with peanut butter frosting, I was making over 300 cupcakes and my frosting broke! EEK! I was able to rescue it by adding some softened cream cheese, maybe 2-4 oz.
I have always used butter in my PB frosting and it never broke. The key is to not overmix. when it is combined, stop mixing. Seriously.
Hope it helps.
December 5, 2013 at 10:46am