SORRY_SORROW_SIN Cupid's Corner is a dating app that comes with Lovestruck. If you don't have that pack, your game doesn't download sims for the app.
What it sounds like to me is you aren't saving the household before exiting CAS. When you start a new game and create a sim, the game autosaves the household to your Library when you exit Manage Households. It is the only time you get an autosave with/in CAS. I'm not sure when the autosave occurs but it looks like it is happening for you after you've edited the 1st sim, probably when you hit the button to create the 2nd sim.
So, I suggest you hit the save to Library button when you finish editing the 2nd (or 3rd, 4th, etc.) and before you hit the check button to exit CAS. It is in the upper right corner of the screen.
Hope this helps.