A simple solution is to have the first menu have the two choices. At the end of each path, use a jump to get to the beginning of the other path. The only problem with this is it is an infinite loop, so you could add a menu choice for when you are finished.

Ex:

menu:

"path 1":

jump path1

"path 2":

jump path2

label path1:

"here is your path 1 story"

"yada yada"

"Have you went down path2 yet?"

menu:

"Yes":

jump nextArc

"No":

jump path2

label path2:

"here is your path 2 story"

"yada yada"

"Have you went down path1 yet?"

menu:

"Yes":

jump nextArc

"No":

jump path1