@Unexpectedlysinglemum It sounds to me that @Dazedandfrazzled has sadly got the "ICK" after all this time of him seemingly being unable to do anything any faster, whatever the reason for that might be.
My husband is similar, and the reason for his behaviour correlates completely with when he got his first smart mobile! Say my DH is cooking dinner, he will put something in the oven, then set a timer on his phone for when the vegetables need to be put on to be boiled or microwaved. As soon as he has set the alarm he will get immersed in his news app, or online cycling group etc. When the alarm on his phone goes off he will cancel it, then think something like 'I will just finish this article', and 10 or 15 minutes can pass before he finishes his article. Or, quite frequently he will forget all about what he was supposed to be doing, and go onto the next article.
He is like this with almost everything - even getting dressed, he will put his pants and trousers on, then sit on the edge of the bed looking at his phone, before he goes to find a shirt - not easy for him as he prefers to keep his clothes in a pile on the floor rather than open the wardrobe door and hang it in there.
Once he has his shirt on he will sit on the bed again to put his shoes on, then before he stands up to go and find a chair or something to make it easier for him to tie his laces up, he will just have a 'quick look on his phone' - maybe he is checking that there isn't a nuclear bomb rapidly on it's way to nuke us in the next 4 minutes, in which case it would be pointless to bother to do his shoelaces up (I would have to reluctantly agree with him on that particular judgement call). I don't think I had better add anything more, other than to mention the words "don't get me started on how long it takes him in the bathroom" 🙈
So I cannot blame the OP (You, if you are reading this "Dazed") if she has got a massive ick locked into her brain and heart, after his, what appears to be, very selfish and disrespecting behaviour towards the OP. If the OP has been inflicted with this soul destroying attitude, then I have no idea whether their relatioship has any chance of recovering or not. However, I do think that if she (the OP) wants their relationship to have any chance of surviving, then they need to access some joint counselling, and probably some individual counselling for him as well.
Good Luck @Dazedandfrazzled. I would love to be able to send you a big bunch of 💐 and an even bigger hug - if you would like one! Please take care of yoursef, and if possible, talk to a trusted friend face to face, to discuss any realistic future ways forward xx