22 20 + 1 = 21 bytes
Takes delimiter and strings as command-line arguments. Uses
-n flag to print output values on separate lines.
g is list of cmdline args; s is space (implicit) POg Pop the first item from g (the delimiter) _@? Construct a lambda function that takes a string and returns the index of the delimiter in it Mg Map that function to each remaining item in g Y Yank the resulting list of indices into the variable y (MXy)-y Take the max of y minus each element in y sX Space, repeated that many times... .g ... concatenated to each item in g Print, newline-separated (implicit, -n flag)
And an example run:
C:\Users\dlosc> pip.py -ne Y_@?POgMgsX(MXy)-y.g , "Programming, Puzzles" "And, Code golf" Programming, Puzzles And, Code golf