You might start seeing your relationship with your lover as an obstacle to your chosen work, because the way that they lead their life is in direct conflict with the way that you need to advance in your career. Maybe you need to be out there in the public, networking with the VIPs, promoting yourself and creating a very specific and well-crafted image of yourself...and your lover just wants to stay home. Perhaps you need to travel a lot to get your career off the ground, and your partner needs to stay rooted in one spot in order for their work to work out.
They have needs that could turn into demands or even ultimatums when they aren't met. You have to come to some kind of agreement, but that isn't easy, especially if bad feelings have sprung up as a result of your different aims in life. You might both end up having to ignore the issue altogether if you want things to work out between you -- just don't talk about work at all. But that's no fun, and it's hard to ignore such a big part of both your lives. If you can move past any hurt feelings -- even if it seems to your lover as if you put your career before them -- and talk things out, you might be able to strike a compromise that works for both of you. It takes a lot of communication and dedication from both of you. If the relationship's just a short-term liaison, it might not be worth it.