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Speaking as someone who has been where BF is at (back when I was an immature, clueless young man), BF is an immature, clueless young man. He'll probably outgrow his immaturity but, unfortunately, that's years down the road right now. For the foreseeable future, he'll keep picking at this emotional wound. I really feel sorry for the guy because what he's going through is very real and very painful. But it's a hell of his own making.
For the LW, I would tell you that there's nothing "sacred" going on with BF; that's just guy BS trying to articulate reasons for irrational thoughts and behavior. He only has one course of action that's consistent with his stated beliefs and actions: leave the relationship. But that entails voluntarily giving up sexual relations with the LW. An immature guy isn't going to make such a mature choice. LW might try making that choice for him by cutting him off sexually. There's a lot of perspective to be gained when sex is taken out of the picture. At the very least, it'll precipitate some serious, heart-to-heart conversations. It might help and probably can't hurt.
However it turns out, I hope the LW doesn't take ownership of this "problem". It's entirely the BF's problem.