I'd go with the yandere route. I know it's objectively the more dangerous choice, but at least there's one thing you can count on with a yandere: they genuinely, absolutely love the protagonist. No worrying about their affection dropping, no sudden change of heart, no getting dumped because they fell for someone else. If anything, their behavior gets more and more unhinged precisely because their feelings are getting stronger. In other words, the love is guaranteed. If I look at it that way... well, I suppose a little stalking and possessiveness are just the price of admission.