Two people may meet through an activity after work that they share with friends, so it might take several dates before they discuss where they work or what they do for a living. They might have already established they have common interests and goals, but finding out they are dating the competition in employment can be difficult. It does occur on occasion, and it can be a minefield for those experiencing it.
There is nothing wrong with dating a person working for a competing company in the workplace, but it might raise questions of loyalty at the office. Being able to state categorically that it will not interfere with work should put the questions to rest, but some companies do find it troublesome. Only time will prove their loyalty to the company, but the couple will have to learn how to keep their work completely separate from their personal relationship.
Compromise is always important for two people dating and forming a long term relationship, but this one will require a bit more work on their part. Each of them will have to remember that discussing their work should never be part of their relationship. It can wear on them over time, but doing it successfully can keep them from the choice of their relationship or their career.
There are other ways they can compromise, but it often entails finding a new job for at least one of them. That can place a heavy burden on the relationship. The person who chooses to find a different job may harbour resentment that their partner was not willing to offer to do it, or they could find their new job less fulfilling. Being able to work past that is something the two can discuss, and it may help them make the adjustment if their relationship is going to survive.