First off, to answer your question directly. I would create a true/false variable for each of your topics with the initial value set to false. This is for whether or not the user has visited those particular pages.
Then, on each of your video layers that end each of those three topics, you need to do two things. Add a trigger for when the video completes that sets that topic's variable to true. In the example below, we are watching the materiality video, so we set the materiality variable to true.
IMPORTANT: Make sure your adjust variable trigger occurs before your jump to slide trigger or it will not trigger. (I have made this mistake more times than I can count.)
Then adjust your jump to slide trigger to match the one in my example below. You will set the primary trigger to take you back to your slide 1.1 if all three variables are true. Otherwise, it jumps back to the dividing path for these three topics.
Second, a recommendation after skimming your storyline. I understand the desire to use the checkboxes to mark off each topic as the user visits them. The issue arises if a user decides to re-visit one of the topics. Currently, it unchecks your check boxes and then sends them off. This could get confusing to the end user.
My recommendation would be to replace the actual check boxes with an image of the empty check box. Then use the states for the image to have a box with the checkmark in it. Then on your menu slide create a trigger for each check box for when the timeline starts on this slide, set the state of the image to the checked state if the variable for that check equals true.
So, for example, if they click on materiality, they will go through the materiality topic, click on the video, then the video ends, the materiality variable is set to true, and the user is deposited back on 1.5. When they arrive, it checks and materiality=true so the checkbox image next to materiality is set to the checked state. Same thing for the others.
