Even if you didn't start out being overly traditional in your values regarding commitment, duty and so on, you became more so in this relationship, in part because of your lover's rebellious insistence on independence. Over time it's become apparent that you need a lot more security within the relationship than your partner does. The bad news is, your natural response might be to cling tighter and tighter, which only causes your freedom-seeking partner to run even more determinedly in the opposite direction.
The gulf between you became wider as your perceptions of each other solidify -- you take on the role as the controlling, overly needy or demanding partner, while they're the rebellious and unreliable one who can't be counted on. Neither of these characterizations is exactly fair; it's just that you bring out these qualities in each other, because you're both naturally looking out for yourselves and your own interests in the relationship. When it starts to seem like you're not getting what you want, you naturally respond by insisting on it, instead of taking a softer approach. The blending of your strengths and seemingly opposing qualities have a much better effect. It might be that all your struggles over this subject leads to a forced compromise. It's up to you to make the compromise come true.