This aspect isn't an easy one to deal with, and part of the problem is that you both might feel like you're fated to be together -- like there's a karmic bond between you that makes all the suffering you put each other and yourselves through worth it in the end. You find that you come from two completely different sides of the fence, and your differing life experiences have led you to become two extremely different people. Instead of being able to enjoy all the myriad ways in which you're each an individual within the relationship, your partner, especially, is more likely to try to control you in an attempt to make you into someone that's more recognizable to them.
You have a hard time feeling light and natural together. Any playfulness definitely has to come from other aspects brightening up your relationship, because if it's just up to this one, you have a very heavy, serious bond indeed! You could stay together out of a sense of indebtedness, as if you owe each other something -- but what? If you feel this way, you should definitely take a look at your motivations for staying in the relationship. While it could be that you both derive some sense of stability out of the seriousness of your bond, it's more likely that you both just stay in it out of a misguided sense of duty.