Haven't done this in a while, so I just looked on wikipedia. This is what it said (for expected value):

Expected value - Wikipedia, the free encyclopedia

result is valid even ifXis not statistically independent ofY.

So in your case E(Y - X) = E(Y) - E(X).

To find your V(Y-X), you'll need to use the following property:

Variance - Wikipedia, the free encyclopedia

since in your case X and Y are not independent, their covariance is not 0.