Is it acceptable to fall for someone else when you are in a relationship?

I will elaborate. You are in a relationship, and suddenly you meet someone (let’s say, a new coworker) and you hit it off platonically at first. Maybe it starts just as a friend crush, but it progresses to the point you could see yourself happily in a relationship with this person. If at some point you realize that theycould potentially make you happier than the person you are currently with, is it acceptable to break up with the person you are dating and move on to this new flame? There is no cheating at any point, just friendly flirting. I guess the question is more: Should you keep your options open, even when you’re in a relationship?

Is it unacceptable? On one hand, I understand loyalty and not sizing up every person you meet for how they might be for you to date. On the other hand, you have to make yourself happy. So many people find themselves in relationships that drag along, get them down, but they’re in a rut and it’s hard to get out. So shouldn’t you be able to keep your options open?

Would you end a relationship to start a new one with someone you felt was better for you? How would you feel if your SO broke up with you for this reason? How soon are you supposed to tell your current SO that you want to end it with them and start anew with someone else, without jumping the gun? What do you think?