Tell one of them to stay longer after they break in, be excited at the start of the second date, tell Tenebris you won't be held back + lot's of choices in the favor of one of them.
tried out many options on the second date and third date
spoiler:
after accepting Tenebris for who he is, I get a cute ice-cream date in that place where he tells the truth about himself. and still get the same two endings after the third date.
If you pick all the things I listed above and have enough points with him, you should go down to investigate after getting a call on the interphone. There will be a second option once you find Tenebris.
