Some big man-hugs for you man, you sound like you could use a few. I understand how a "just grit my teeth" can really let the air out of your tires. Who'd want to ML with someone knowing that person is gritting their teeth waiting for it to be over. Sounds more or less like the definition of rape to me. If she's going to act like it is when it isn't, then why ever take a no from her, just do it whenever you have the urge whether she wants it or not (maybe that's what she secretly wants, I seem to recall you mentioning she got horny watching some movie where the Marines were taking what they wanted)
I'm with Choc here, I think a simple "Thanks for letting me know how you really feel. I'm really sorry you feel this way" and leave it at that. It sounds like it is time for you to start seriously rethinking your options.
