I read the whole of that other thread and the relationship the OP described covered most of the things that have been posted here apart from the statement that she didn't love him. In that context I took this to mean not dizzying, romantic, sweep you off your feet mode which is really infatuation, not love (though it can turn into something lasting and deeper).
I've been reading these threads looking for an answer myself. The same age as Snowdrop (63) with a 34 year marriage, I am bewildered by how things have changed in the last year and I wonder if she, like me, is finding it hard to believe and keeps hoping that the relationship is ok or good enough.
We've had massive changes, children leaving home, some emigrating, moving house and downsizing, me retiring, him semi retiring but now working from home so he's always here. We've certainly had our bad times but the tension now is awful, arguments break out all the time. He's always been rather quiet and passive, but he's become passive aggressive with lots of little digs and asides and if I challenge him he denies what he said or insists I am mistaken and that isn't what he meant at all.
I've just had the loveliest day with my daughter and was so happy and since we came home he's been sniping about what I did in the garden yesterday 'without his input' (he was actually not here), about how i am a busy bee when he's not here or for instance, about the fact that I often sleep elsewhere because of his snoring, the list feels endless. I don't recognise the man I married, I'm sure he didn't do this in the past and I wonder about depression and dementia (his mother had it) and all those other things that people suggest might be happening. I feel that he tries to control me, he interrupts me when I'm speaking, tells me I'm wrong, corrects me about facts and things I might say that he disagrees with, sometimes in front of other people. If I complain about this later he'll say he doesn't remember or that wasn't what he meant at all. The other day in the car he wouldn't give way at a narrow point in a lane to a car coming uphill. The other driver eventually forced him to and he grumbled so I said 'well the rule is to give way to drivers coming uphill'. He said nothing for a moment and then insisted that the other driver had had plenty of room.
He's flounced off now, after a tense evening he started rubbing my leg in bed, I asked him why he pretends everything is ok so he's gone to sleep elsewhere while I sit up feeling miserable. And the cat, who will no longer stay in the same room as us both, has gone to sleep in the garden. It's not marriage is it and it's hard to believe that and to take that step of packing the bag and meaning it. I don't know any more what's real and what isn't. I don't know how to leave and I keep thinking maybe it's alright because sometimes it is. I do admire people who can be so clear. How do you know and are you just fortunate that things haven't got so bad.