I also believe that NPD is not an involuntary behavior and that the NPD becomes Bipolar (eventually changing their brain chemistry because of the long-term habit).
You weren't FORCED to avoid walking all over him, but you did avoid doing that because you are true blue ("true blue" is your perfect match, good luck finding that without "nice guy"). The combination of "nice guy" and "bad boy" simply doesn't exist outside of Hollywood films where they deal with reality for only 2 or 3 hours at a time.
What nice guys have to understand is that they have to know that people will choose to have them become "convenient" when given a chance. Sometimes friends or romantic partners appreciate a nice guy being convenient, but when it comes time for the nice guy to be protective or "take a stand", the nice guy has developed a bad habit of being nothing more than a doormat because of always being encouraged to be a "nice guy".
A good relationship is built on both partners LEARNING from each other. A truly nice guy WHO HAS learned to respect himself (because he is treated with respect) will not let anyone walk all over him,...including his romantic partner (this is the part you might misunderstand sometimes, but in order to be protective of you, he needs your understanding on this). This should NEVER include control over you (or any kind of "power play").
It's the bad boy jocks (ego, control) who are the NPDs.
OBJECTIVELY speaking, "equality" among the two genders is a myth (male and female lifestyles are different and cannot really be equal). "RIGHTS" can be equal, but only if you give him the right to wear your clothes, makeup, etc. (or were you referring to "fairness"?, ideally, there should be no imbalance of that, but it's not a BUSINESS relationship, it's supposed to be a LOVE relationship, no power).
With PROPER AND EFFECTIVE communication being the norm in a relationship, you might often find each other able to finish each other's sentences (this is a good relationship).