Whenever you start to doubt things, he tells you how silly you are... he tells you this excuse for a sex life is normal and that your expectations are unrealistic... he tells you lots of things, but what you need to realise is just because he says them does not make them true. He is either lying or deluded.
You are used to turning to him for advice, guidance, support; on the spot, in the evenings when there's only two of you there, you've got no-one else to turn to when you want to talk things over; so you're used to going by what he says. You're in the habit of accepting something is true because he's told you so, because he's intelligent and he can make a good argument. He's also had a lot of years to observe you and know exactly which buttons to press.
Please, step back for a moment and realise that he is not right about everything. He's older than you, maybe better educated (though you sound far from stupid), but that doesn't make him automatically right about stuff. Particularly stuff you know in your heart of hearts is wrong, but you can't somehow convince him of it, and eventually you give in because you don't want to upset things. Like when he accuses you of making him do a job he hates, and you know that's simply untrue. Or that you refused sex when you were actually begging him for it. Don't tell me he really believes that you did, or that if he does believe it, he is quite sane.
Whoever told you that companionship is the best you can expect from a long term relationship (who did tell you that? was it your mum? could she possibly be justifying why she stayed as long as she did with a drunken asshole?), well companionship is a great thing yes (though by no means the only thing!), but it should make you feel good. And yours simply does not. Admit it to yourself, and this time, stop going "yes but..."
That's the cognitive dissonance thing someone mentioned earlier. Where you convince yourself something is ok really, even though it clearly is not. Someone outside the relationship - lots of someones in this case! - will say Oh my god, that is awful, but instead of agreeing you start in defensive mode, justifying why you are still there, basically. And then you end up even convincing yourself. It's hard and painful to get your eyes back in focus and see the extent to which you're being controlled. For a while, as an intelligent person, you will likely be damned embarrassed at what you have allowed him to do to you. At the lies you have believed, and the ones you've told yourself. You have to forgive yourself for that. Your mistakes are understandable and the reasons you did what you did made sense at the time. But they were mistakes, don't you see? They were lies. And once you start to see manipulation for what it is, it will never work on you to the same extent again (though it may take some time to change your reaction to all of the triggers).
Then, and only then, you can tell whether you want to leave, and will know that it is your choice.