Even though you want your connection to be lighthearted, something always seems to drag you both down when you're together. You have a deep emotional involvement from the start, but it is a heavy one, one that doesn't always bring you a lot of pleasure. After a while, your lover, especially, might start to realize that they feel a sense of burden when you're together, one that lifts when you're apart -- and they might not even be able to pinpoint where it's coming from.
But it has a source: you try from the start of your relationship to get them to change, and the pressure from this wears on both of you after a while. It starts out subtle, and they might not even mind the minor adjustments that are being asked of them. But after a while, they might start to feel like they can never just relax and be themselves. You constantly tell them that they're not doing things right -- maybe they're not dressing right, or treating people right, or cleaning the house right or... The criticisms probably aren't huge in themselves, but they amount to a general feeling of being chronically unhappy and dissatisfied. The funny thing about this tendency is that your lover actually really might need to change their behavior. But if they're forced to do it under pressure and criticism, instead of slowly and at their own pace, this could be a rather annoying influence to deal with.