I should consider myself lucky for having a twin. My twin has enough tact to keep quite about my habits and do what she was going to do if she ever caught me jerking off.
Some people had a hard time understanding what was happening in the first parts of that route (mainly because of the translation, they said) but try to endure it and enjoy. :3 You'll understand it, eventually
The choice after the beach part will be the last choice you will see for the common route. (I think?) Then after 30 minutes or so, you'll see the second op. And you're locked on one of the girls' routes