This person has a hard time meeting your needs, though they genuinely want to do so. They try their hardest, putting your needs before their own, but nothing they do is ever quite enough -- and they could feel used and taken advantage of after a while. It isn't that their efforts aren't enough, but more that they're misdirected.
They just don't understand very well where you're coming from, so it's hard to figure out how to make you feel good. What each of you wants out of a love affair is likely to be very different; one of you might want a lighter, more humorous, friendly attachment, while the other wants something serious and emotional. In that type of scenario, neither of you really gets what the other wants, and you feel irritated as a result. In fact, the small irritations of your day-to-day relationship are what build up over time and cause the most problems. Your tastes differ so much that if you live together, for example, or work on a creative project, you have a really hard time settling on anything that you could both be happy with! Though disagreements over your personal aesthetics might not seem hugely important, somehow, the arguments take on a significance of their own, not to mention the fact that it's so hard to get along. Other more harmonious aspects help mitigate the difficult effects of this one.