I am having a bit of a moral conundrum that I would appreciate some external insight sifting through.
I've been in a relationship for years with someone who I've known for some time to be a master manipulator. He is incredibly patient, amazing with language, and can manipulate people so subtly it's almost impressive. As a moral rule I would find this detestable, and I have for most of my life been a strong advocate for breaking free of manipulative relationships. But in my experience with him, he has used it entirely (that I've seen) for purposes of good... not limited to planning a surprise wedding, guiding people out of abusive relationships, etc.
There are times when I can sense that I am being manipulated, and I don't dare say anything because it will cause a fight without fail, but I generally don't worry too much about it because these manipulative tendencies have never come to any negative ends in our relationship (that I am thus far aware of). In fact, I've made incredible leaps in my personal development by allowing him to guide me down certain paths, including helping me break free from substance abuse. The subtle way he can guide you through new thought patterns is a gift, but the ability itself is suspicious.
I love this person, but this knowledge has been weighing heavier and heavier on me. A dear friend is currently escaping an abusive relationship, and she told me, point blank, "I cannot be around [my partner] right now, even though he's a dear friend, because he is so manipulative and I think interacting with that will be a trigger for me".
Hearing this really shook me up. I've never heard anyone else acknowledge what I already knew about this person. It was one thing when it only affected me (and generally positively even if concerning), but I'm becoming concerned this problem may have deeper roots than I'm aware of.
So I am torn. Do I uproot a happy and functioning relationship?
Is manipulation an unforgivable character trait?
Am I enabling by not standing up against this character trait?
Especially early on in our relationship, I did attempt to address this issue. You might say he "manipulated himself out of addressing the problem", but he makes the strong case that...it isn't really a problem? Is it a problem if no one gets hurt? Or is it wrong by its very nature?

Any thoughts highly appreciated...