A friend once compared dating to being underwater.
He said: "When I am with someone, I feel like I am swimming underwater - it's fun, refreshing, and it feels good. But if I do it too long, I start to feel trapped - I need to come up for air. I'm not built for being underwater - I have no gills!"
Let's stretch this metaphor a bit further, shall we? Different people like to swim in different ways - some like to splash on the surface, only occasionally dipping underwater (analogous to those who remain single, but have a lot of first dates); others stay under as long as they can, only coming up for air when they must (serial monogamy). Some people find the air to be cold, and like to stay underwater; others are afraid of being submerged. Most people fall somewhere in between.
I've heard this sentiment expressed many times - more often by males, but also by females. The metaphor (and, I think, the feelings behind it) includes a sense of being trapped. People drown in water. Likewise, people feel suffocated and trapped in relationships.
How does one resolve these feelings of being trapped? The obvious answer is get out of the water. If you feel the desperate call for freedom that strongly, perhaps it is best if you live your life alone, safely without anyone to hinder you or your actions. Not everyone is cut out for pair-bonding.
However, I feel that a better way is to change yourself. Accept these feelings of being trapped - if you are male, you may just be feeling your instincts acting up. Once you acknowledge these feelings as a normal part of the pair-bonding process, it is much easier to change the root causes. Yes, you will have to change, but so will your partner.