If you were going through life living out comfortable routines, that all got shaken up when you entered this relationship -- no matter how long ago that was. The way you usually did things flew out the window, and you're now called on to change along with the relationship. Even if you both try your hardest to keep things smooth and seemingly 'normal,' affairs just have a way of slipping out of control of their own accord.
Your partner goes through big changes and dramatic emotional displays, while you're busy trying to resist the changes and hold onto the status quo ... After a while, it's become more and more obvious that this dichotomy doesn't work. You can't hold on to the way things are while progressing together as a couple, or as individuals. You both have to dig deep and figure out where the incompatibility is occurring. Do you have similar styles sexually, or is your partner always shocking you with their deep passion and abandon? Are they pursuing a career that feels unseemly to you? Or do they just have a much more varied and transformative emotional life than you do? Wherever the differences lie, as you look at them honestly together, you can find out how to learn from each other and grow together.