Re-reading all of your posts in this thread, I notice there are recurring themes of guilt, shame, low self-esteem and stress (I'm guessing the stress is mostly caused by the other emotions).
Your OH telling you her fantasy is to cuckold you, she hasn't been keen on sex since you met and her admitting that she has been withholding sex from you cannot be helping you with those problems.
I think if I were in the same situation I would have the same feelings, though they would probably manifest in a different way.
Her themes from your comments are that she finds the masturbation (and therefore you) disgusting, and lacking in intimacy. This may go a long way to explaining the withholding of sex and the desire to try another man.
I think the lack of uncontrollable erections yesterday was not so much a sign of you being satisfied but more a sign that you actually felt good about yourself for a change ("but hey - look at us!!") I can almost see the grin! The masturbation last night while rereading what you'd written was just 'normal' masturbation, reliving some great sexual experience and getting horny as a result.
Her desire to cuckold, the way she blind folded and made you restrain your hands, asking how you feel about restraints, the pleasure/punishment cycle she took you through; these things all suggest she is a dominant personality, or at least wants to explore that side of herself.
You seem very open to the idea, it gave you great pleasure, the idea turned you on and you said the idea of restraints was more to your liking, you're now even considering getting some wrist restraints. This suggests you are a submissive personality, or at least like the idea enough to experiment with it.
Sounds like a potential match made in heaven to me! The vital ingredient missing is communication.
I think you two need to talk, openly and frankly about this. Let her know that what she did last night was so good it stopped you from masturbating all day. Tell her you liked it and want to let her explore her dominant side. Explain that you cannot be expected to not pleasure yourself if no one else is going to do it for you.
Taking all this one step further; have you considered male chastity devices at all? She could lock you into it in the morning and would know you couldn't pleasure yourself at all for the day. In return for being a good boy all day she could agree to 'release' you in the evening, in any manner she chooses.