measuring bankfull width by distance between points

I have a large set of polygons that represent sections of streams, each of which has a Unique ID. Each of these polygons is made up of a series of left bank points (LB1,LB2,etc.) and right bank points (RB1,RB2,etc.). I need to calculate the average bankfull width (width of polygon) for these streams.

I think something like point distance in arcmap would work, but instead of finding the distance based on nearest point I want to match up LB1 and measure the distance to RB1 and sequentially do this for each set up bank points.

Any ideas?