WARNING - LONG! Whatisreality, you need to stop making excuses from him to yourself. You say he is shy, gets a lot of headaches, etc. Well, my DP has Social Phobia and gets regular headaches and he treats me like I'm a Queen. Being with him makes me feel better about myself and my life, never worse.
My Ex, however, reminds me of your DH on a much lesser scale, as he used to tut and roll his eyes at totally mundane things I did, like blow my nose or chat briefly with a checkout assistant at the supermarket. He also used to accuse me of having emotions that were totally different from what I was actually feeling - telling me I was being moody and aggressive, when I was actually happy and carefree - or accusing me of acting in ways I wasn't, doing things I wasn't, etc. And all his bad moods and problems were somehow caused by me, even things that had annoyed him at work! He used to make me feel like I was disgusting and repulsed and disappointed him in everything I did, said, wore, etc. His sexual dysfunction was that he never wanted to have sex (although I did discover that he looked at hardcore BDSM online) but if he did, he wanted to only do it in a particular position that he knew I found painful (not a weird one). So I refused. I never believed his crap but it still destroyed my confidence and I still have much lower self-esteem than I used to, so I can totally understand how hard the thought of leaving must be for you. I also understand the need to try to find away to make these sorts of men approve of you and find you attractive, treat you like an equal, truly 'see' and understand you, but believe me - they never will. The problem lies with them. They are broken and deeply damaged and they are transferring all the hatred, disgust and disappointment they feel about themselves onto you. You aren't real, you are something through which they can transfer their demons onto and punish.
It's very, VERY telling that the people who know you best, your brother and your best friend, dislike him and think he is no good for you. They understand. They can see the truth. When people see the truth and tell you it, listen to them.
A huge factor in your prob is the sexual aspect. Now, I'm a live and let live kinda gal and if a couple of any sexual persuasion gets their kicks from bum fun, then good luck to 'em. It's not my bag, but it's none of my business. However, your sex life is not working for the two of you. It seems incredibly dysfunctional. Me and my friends are pretty frank about sex and I have never come across a single woman whose partner or husband asks them to rim them (lick their anus). And certainly not to the extent that you are expected to. Hell, a few of my gay friends hate rimming and being rimmed. I worry that as he is your only sexual partner, you think his requests are pretty standard and they aren't.
A comment you made about your parents struck me - you say that they have sex every day. this worried me for 2 reasons. 1) How do you know this? If they have not adequately tried to hide this from their kids or talk in detail about it, that is having weak sexual boundaries from their children, which some psychologists call the very lowest rungs of abuse. My parents are v open about sex, etc., but I've never heard or seen them (ie barging into their room) doing it and they don't discuss the frequency or anything like that. If this is the case, it will have weakened your sense of sexual boundaries and 'normalcy'. 2) Have you ever considered that your mother might not want sex every day but daren't say no or says yes for an easy life? If this is the case, it could well have conditioned you into unconsciously believing that women are supposed to give into their partner's unreasonable and unappealing sexual demands.
Last question: are his parents still alive? If so, what is the relationship like between his parents? I wouldn't be in the least surprised if you said his father was similar and his mother is a timid mouse of a woman, possibly with depression or other mental health issues.
I know this is a bloody epic, but I am so worried about you and really want you to see that this man is abnormal, totally toxic, deeply troubled - and that you need to leave him. I left my idiot Ex after 7 yrs when I was 33. I met my DP when I was 34 and we are blissfully in love, living together and expecting our first child now (I'm nearly 38). Something or someone better WILL come along... because you cannot do worse than what you've got right now. YOU need to save yourself and be the person you need. You've gone from not-great parents being in control of your life to this bastard being in control. Now's the time to be in control of yourself and your own life. Good luck.