Spending time with Oliver or Merina can still get you the neutral ending, but not the best ending.
Acting like a slut while also being as faithful as you can to Tate will let you have the best ending :)
That was me. I never want to get the bad or worst endings again. The worst ending for Tate's route just shook me up and left me crying for about 2 hours rambling on about how it all broke my heart. Always going for the best stuff; keep it up, this vn is the best one I've ever used... AND I LOVE CODY!! >:3