Though you might have a very demanding career that takes up a lot of your time, interest and attention, that shouldn't hurt your relationship with your partner. In fact, your work is important to you, and it becomes very important to your lover as well. They really identify with your career success, and they want to support you as much as they can in pursuing that success.
The encouragement and willpower that they are able to drum up for you is nothing compared to the sense of energy and you-can-do-it confidence that you experience due to their unflagging belief in you. They cheer you on during the rougher times and are there to celebrate all your achievements, and success for one of you is success for both of you. They are your safe harbor, your rock, your cheerleader and your shoulder to lean on when times get tough. It's even possible that you end up working together, whether that means in an office or as a team at an important function where it's every bit as important to network, meeting and greeting potential clients, investors or other supporters, as it is to deal with those clients, investors and supporters during business hours.