On a subtle level, there is a mismatch between you regarding how your lover experiences the world on a day-to-day basis as compared to where you need to go in life, on a grander scale than just the everyday. Say your lover likes to stay home all the time, watching TV. There's absolutely nothing wrong with that, but it could make things difficult for you if your goals in life include travel, getting out into the world, instead of staying home and watching it pass you by on the tube.
This is the kind of struggle you two experience. It may not be terribly overt, but you both feel the tension that results. If you are a committed couple, for you to feel comfortable, as if you're doing what's right for you in your life, your lover has to be pulled out of their comfort zone and into yours. That is hard for both of you. You probably wonder, why you can't just blend your styles and needs and work this out, but that's easier questioned than achieved. Blending just might not be possible. Instead, you might have to talk things out openly and honestly, and see if you can't learn to understand each other's goals and ways of experiencing life -- and then allow each other to be the people you are, instead of whoever you each wish the other were.