Love Tester Code Golf
Pyth, 40 bytes

jd[z"and"Jw"have"/K-lzl.-rz0rJ0i=J*lzlJK"out of"/JiJK"chances of love.


The code is 70 bytes long and qualifies for the -30 bytes bonus.

Try it online.

  [                        Begin an array and fill it with the following:
   z                         The first line of input.
   "and"                     That string.
   Jw                        The second line of input, saved in J.
   "have"                    That string.
           rz0rJ0              Convert both lines to lowercase.
         .-                    Remove the characters form the second string
                               from the first, counting multiplicities.
        l                      Get the length.
     -lz                       Subtract it from the length of the first line.
    K                          Save in K.
                  =J*lzlJ      Save the lines' lengths' product in J.
                 i       K     Compute the GCD of J and K.
   /                         The quotient of K and the GCD.
   "out of"                  That string.
   /JiJK                     The quotient of J and the GCD of J and K.
   "chances of love.         That string.
jd                         Join the elements, separated by spaces.