@Striffee True, why have a harem when you're only going to end with one. Stories like that get's dissapointing because you build every character, their relationship and romance, but then throw them out.
Just make it into a one true love romance if you're going to end with that anyway. They're basically just baiting an obvious plot twist. And if you do have a supporting role that also likes the MC, make it so that the feelings truly become unrequited, then prepare a partner for them. Develop their relation. Make it that fans can clearly ship them.
The story is supposed to be entertaining, not PAIN. Even tragedy stories have a satisfying ends most times... some stories these days have very dissapointing endings.
The only thing I can do is hope that it's good.