Certainly you can choose not to follow a potential passion, not to make room for it in your life. In fact, if I were to attempt monogamy, I think I might well retreat to Austenian standards of decorum -- never being alone with a potentially interesting person, for example. Never discussing certain topics. Putting structures in place to support the conscious choice I had made, to be with one person, and one person alone. (Actually, I would apply the same argument to celibacy, if for some reason, probably spiritual, I felt strongly called to make that attempt. Or to polyfidelity.)
I can see the value in dedicating oneself wholly.
But that said -- I don't know if it would always work. I'm not sure if all the effort in the world will necessarily be enough to save you, should the stars align against your choice. You could refrain from action, given sufficient willpower, but could you refrain from a broken heart? The world is wide, and it feels almost arrogant to me, to say that you know what it (and you) are capable of.
I'm not saying never make a commitment. I think it's great that people commit to grad school, to jobs, to parenting, to romantic partnerships. But with most things, even if you make a commitment, there are clear outs. People drop out of grad school, they leave jobs. Children, I'll grant; I expect a pretty serious level of commitment from people who decide to be parents -- but clearly, a lot of people are willing to walk out on that too. Which often infuriates me, but that's a separate issue.
I think I see romantic partnerships differently because I wouldn't want the commitment if my partner no longer wanted to be in it. I'm fine with marriage as a statement of serious intent (this is my plan, and I will work seriously to follow it, even when it becomes hard), but the idea of marriage as a promise bothers me.
If Kevin came to me and said that he knew we'd planned to be together 'til we died, but his heart just wasn't in it anymore -- that he had tried his best to still want to be with me, but someone or something was leading him elsewhere, and that he would stay if I wanted him to, because he had promised that we'd be together forever -- it would be incredibly upsetting, of course. But I would hope that I'd also tell him to go, without recriminations. That's my ideal, anyway, personally; I don't know if I could actually live up to it.
How sad, to have someone stay with you, only because they once said they would. How could you live with that?
I think part of what's hard about this idea is the thought that your beloved is leaving you for someone else -- does it change things if it's not a person, but something else? A calling, of some kind? To religion, or a political cause, or a professional passion?
There's a structure in Hindu philosophy -- the four stages of life are student, householder, retiree, renunciate. I find it fascinating that that culture has as a default the idea that there is something after partnership -- that in the end stage of life, you are supposed to leave partner and home, leave the world of material objects, go to a temple or into the woods, and seek a more spiritual path. (Please do correct me if I'm misunderstanding or misrepresenting this.)
I don't have much spirituality in me, and I can't help thinking that it would be very hard on a partner if you made that choice to renounce when they weren't ready for it. But I can see the logic of it too, and the appeal of going out, alone, into the wilderness at the end of life, to see if you can discover something beyond these earthly things...