A cursor can really only access one row at a time. All that jumping-to-the-next-row stuff is just going to make a mess of things.
try breaking the operation into steps:
first, run a search cursor all the way through to build a list of unique COMID values (we can call the list comidList).
next, itterate through that list making a new search cursor with a query string for that COMID for each itteration. This gets you a set of rows with just that COMID (that pair of points).
Each point has two values you want, eh? (NORTH and EAST)
Run through the two points, making a list of the NORTH and EAST values of point 1 (lets call it pnt1List)
[north_val1, east_val1]
and another list of the NORTH and EAST values of point 2 (pnt2List). [north_val2, east_val2]
append these lists to a new list (pntValList). the first entry will look like this:
[[north_val1, east_val1],[north_val2, east_val2]]
Now append that comIdList to a new list (the bigList):
[[[north_val1, east_val1],[north_val2, east_val2]]]
set all the lists EXCEPT bigList and comidList
that is: pnt1List, pnt2List, and pntValList, to [] (we will reuse these lists in the next itteration)
move your cursor to the next COMID in comidList, and do it all again.
You are building bigList to be a set of nested lists of pairs of NORTH and EAST values for each COMID in the same order as your list of COMID values:
([pnt1List] and [pnt2List] inside [pntValList], inside [bigList]
for example:
[
[[north_val1, east_val1],[north_val2, east_val2]],
[[north_val1, east_val1],[north_val2, east_val2]],
[[north_val1, east_val1],[north_val2, east_val2]],
[[north_val1, east_val1],[north_val2, east_val2]]
]
NOW you can itterate through the COMIDs in the comidList list again, this time with an Update cursor.
the indivdual NORTH and EAST values will be paired in the same order as your COMIDs.
yval1 = bigList[0][0][0]
xval1 = bigList[0][0][1]
yval2 = bigList[0][1][0]
xval2 = bigList[0][1][1]
map of indexes -> bigList[bigList index][nested pntValList index][nested pnt?List index]
gives you the y and x values for the first point pairs
perform your calculations and set your new item values.
use variables for the index numbers inside the square brackets so they incremant properly.