relationships in novels

As many others have said: No, it isn't necessary.

I prefer things to be organic. When I started writing my novels I had planned out a sort of love interest arc because it was essential to my story for the future of it. My cyberpunk novel, however, has a heroine who will not have a love interest except the platonic variety.

Basically, the story is what matters. Unless you are writing Romance novels you don't need it unless the story calls for it. Try just writing your story and seeing if one develops. If it doesn't, that's perfectly okay. If it does, that's also okay. Focus on the story, not relationships.

No, you do not need a romantic relationship at the center of your novel. Or, you can twist it around and turn expectations on their head. Oh, you think these two will get together? Well, guess what, sometimes people who argue really and truly don't like each other and really and truly have differences that cannot be papered over. Or, sometimes people don't realize what they have and squander whatever love they'd had. Or they don't really know how to love in the first place, though maybe they try. Or they love so much that when they lose that person, it makes them hard and violent and bitter. Or maybe you crush on a person but end up respecting their decision to stay with their spouse. Those are all various permutations of romantic love I've worked with. Only once did I have a traditional love-interest-that-ended-well kind of story, out of five novels and a novella.

So, yeah, mix it up. Go wild.