This is an excellent question, and as an aside, it’s always a pleasure to receive a well-written message such as this. I’m afraid that there’s no clear-cut answer for the simple reason that each relationship is unique, and each one combines aspects of two different people’s personalities, backgrounds, and individual preferences. The concern about placing yourself in a particular area of erotic power exchange while maintaining a different persona relating to non-sexual situations is common. I’m probably a great example; most people think of me as a strong person with an A-type personality who likes to retain control in most areas, but as I’ve made obvious here, my sexual preference is one of a more submissive variety than anyone who didn’t know me in an intimate way would possibly imagine.
Here’s what I advise. First, open communication is the key. Any good relationship starts with a period of getting to know one another. It would seem that you’d have no problem making your assertive personality clear to whomever held your interest long before the relationship progressed into a sexual area. Despite that, you need to clearly state that your interest in relinquishing control in the bedroom does not equate to any situation in other aspects of your life. As usual, honesty is crucial. If your partner can’t understand this or refuses to confine your power exchange to sexual situations, it’s time to find someone else.
Regarding your ego, this is simple. You need to recognize that only a very strong person is confident enough to allow a surrendering of control while knowing that he/she is capable of returning to their usual mode afterwards.
Finally, I will say that my relationship with my wife outside of sex is in no way compromised by my sexual needs. The reason for that is also simple: she’s a smart and strong lady who understands me well, and knows that any attempt to take our “bedroom relationship” into other areas of life would be disastrous. So, back to the first point: the key is choosing to be with a person who is flexible and intelligent, and to be honest and open in regard to your specific desires with him/her.