I'm not sure about some of this advice on this thread. There is a fair bit of urging you to blame your marriage, blame your husband, but eight stone is a huge weight gain as you know and there has to be some personal responsibility.
Weight gain impacts many things, not just physical appearance. It impacts the way we live, the things we can do, our sex lifes, our energy levels, our self esteem and how we feel about ourselves, how we interact with others, our social lives. All these things together can then impact who we are as a person. Not for everyone, but for some, a weight gain like this can have much wider consequences. You say you're unhappy with your weight, how does that affect how you behave?
You were fully aware of how your husband felt, and as per above that could be much much more than simple physical attractiveness. I'd take some time out for me. Think about who you are, who you wish to be, how you wish to live, and then do something about it, slowly but surely. The only person who can do it is you, which is why personal responsibility is so important here and not blaming your husband or your marriage.💐