But not even with the walkthrough mod this is hinted.
Also, If you look at the code even if you don't persuade her after the variable is already set right after you cum inside, so something isn't quite right with your persuasion argument.
Code:
menu:
"{color=#17970E}Cum Inside Rita{/color}":
if r_love >= 9:
$ r_inlove = True
else:
$ r_inlove = False
if r_submissive >= 15:
$ r_highsubmissive = True
Wouldn't it be easier to just check her pregnant variable instead of this new one then?
Then your point would actually make more sense and it would be easier for players to know why the dialogue option is disabled if it just said (Rita is not pregnant) and players can see the pregnant flag ingame.
But anyways just a suggestion to make the game more accessible.