There are lots of helpful comments here. There are also, as in most of these sorts of mums Net chats, lots of very black and white responses.
Now absolutely you need to look at those posts by people highlighting things such as coercive control very seriously, and there are some good links shared that you should read. At the same time, it is so very hard in these sorts of posts – or whenever in a situation when you hear only the one view, and that edited and thought about for the audience and to put ones argument across – to really know what’s going on for both parties. You use very emotive words, that are certainly for most of us setting off alarm bells: words such as ‘summoned’ and ‘expect’ and ‘demand’. We, of course, now see some arrogant, probably abusive, arse, lying naked in the bedroom just waiting to be serviced by you. That may be true or it may be that these words come from how you feel (and feeling this is absolutely valid), while in fact there is a far more complex and possibly far less aggressive thing happening. We can’t know. You could well be in an horrendous and abusive situation (and again do read that stuff shared by others on coercive control) or you may be putting your partner across based on how you feel, while only ever raising the issue with him once in a while and then only when the act is wanted, in a sort of, ‘not tonight I have a headache’ way, and your partner doesn’t know that when you say you don’t feel like sex you mean ever, while he thinks this time.
You need to talk about this at a moment when sex isn’t something that’s wanted/ happening/ being rejected.
And you absolutely do need to talk about this.
There are quite a few on this thread who seem to dismiss the other person’s desires completely. Why? A marriage is a relationship and a relationship is about how two people work together to achieve something greater than either individual. Yours are two people living your lives together and, while there will always be some compromise, there should never be a situation that leaves either one of you deeply hurt, unhappy, resentful, or secretly wishing that the other one might just have a car accident this evening…!
Sex is – to most/ some/ many – a fundamental part of being in a relationship. If one person decided to withdraw that from the relationship – when the other still thinks it a vital part of their life and of the partnership - then it will clearly impact the relationship hugely. It certainly isn’t, as a few seem to suggest, just something that the other person just has to get over.
So you need to talk about it properly to your partner. You need to make it absolutely clear how you are feeling – that the thought of sex makes you feel ill, that you dread it, and that you feel that you cannot say no to your partner’s demands / requests for it – and then you ned to both discuss what should happen next, what might solve it, whether anything can - therapy, an open marriage, etc (and you need here to think about your own sex drive here, as you say it goes with long term partners, so do you actually still want sex, but just not with your partner?) - and if there is nothing there, no options left, then he has to decide whether a sexless marriage is something he wants. I suspect not and so you need to split up.
A quick aside on thinking about whether you both split up. There are many reasons people divorce and many reasons they don’t. As a child of divorce – and someone who now watches their best friend continue in a dreadfully unhappy marriage – I would only say that whatever you do, do not stay together for the children. I was far more damaged by the two years my parents tried to make things work (sitting on the stairs hearing them yell at each other, slamming doors, awful words, and nightmares filled with people screaming and shouting, etc.) than I ever was when they actual split up.
There is a second issue in your post(s) though, and that is that you say you have stopped wanting sex in every long term relationship (many???) you’ve ever been in. I think you need to think about that and seek help to address it if you ever want to be in anything lasting and loving.
It is true that our desire for our partners change over time. Sometimes our libidos change with age (though often it’s hard to split our feelings for partners from our general sex drive). It is absolutely true that ‘familiarity breeds contempt’. It is also true (and there will be many here that will attack this statement) that as our partners age and their bodies change we find ourselves less attracted to them. Now, of course, there may be new things there that we find just as sexy – even sexier – and love is always useful too, but these things won’t be the same things that first made us want to pull each other’s clothes off and spend whole days in bed together. And, of course, just as we notice those changes in our partners, so will we be very aware in the changes age has had on our own bodies and, perhaps, our self confidence takes a dive.
Equally, our lives change and our priorities and passions and goals. Companionship and familiarity and the life you’ve built up, and hobbies and friends and children and all sorts might take a far larger interest for us that the physical. But all of that doesn’t and shouldn’t take away from the fact that your desire for sex has completely gone while yours partner’s has not. There should be no blame in this, but it should not be swept under the carpet either. The same would be if two people went into a relationship both talking lots about their desire to have children, only for one to change their mind. No matter how good a life you’ve built, no matter how much love there might be, something fundamental has changed and that needs lots and lots of talking through and may well lead to the death of the relationship.