My mum stayed with my dad for the sake of the kids (me and one sibling).
The relationship model we had was so dysfunctional we've both gone on to have shit relationships ourselves. Add the guilt of knowing mum was unhappy - and for me as I got a bit older, like 10yrs onwards, being her emotional sounding board, crutch and surrogate 'significant other' meant my view of my dad was tainted and her reliance on me was just too much. I didn't properly separate in the normal way and it was suffocating but I felt I owed her some happiness as she'd tolerated her marriage for our sakes (we had a nice home and were comfortable financially. In her mind, if she'd have divorced we wouldn't have been anywhere near so comfortable).
When I divorced she was horrified that I refused to 'stick it out for the kids..' However I knew the damage that causes. My kids are young adults now, both very happy and settled and both have good relationships with me and their dad. They didn't like the initial separation for a few months but once the new routine and 'new normal' was established they were honestly ok. They had 2 happy parents in 2 peaceful homes. This was far better than 2 unhappy, arguing, shouty parents in one unsettled home. They have a lovely step-mum and half sister from their dad's new marriage (and not a lot from me, I just can't 'do' relationships largely to do with my childhood model).
I'm nearly 50 and am having to come to terms with the FACT that growing up in a weird and dysfunctional family dynamic HAS created a lot of problems for me which I've carried in to adulthood. I literally have no idea what a normal, healthy relationship looks, sounds or feels like. I feel guilty that both my parents have been unhappily together for the last 35 years, I cannot reconcile the man my dad appears to be with the man she told me he was, and my poor sibling is even more fucked up.
In your family it might only be 1 in 4 who is unhappy right now, but once they're adults it's very likely to be at least 3 in 4 who are unhappy. You are showing a really poor example of a couple/partnership to your children, which they will absorb as being 'normal' and may well go on to copy this is their lives. Surely you want better for them? As they get older they'll realise that you aren't happy but might think it's because of THEM and stuff they say or do. It probably won't occur to them that it's their dad as they'd surely think if you're that unhappy, get divorced.
We'd have all been far better off not to have continued in such an unhealthy dynamic.
You, your children and your husband ALL deserve better. Although you don't want to hurt him you ultimately will if you leave in 10/12/20 years time, maybe even more so if he realises you were hit biding your time. And you'll have hurt yourself and your children as well. Kids survive - and thrive - following divorce, it's misleading of society to suggest otherwise and is a rumour possibly perpetuated by people like my mum, to defend the indefensible of stating unhappily shackled.
I'm sorry to go on a bit. And I'm really sorry you are unhappy - you could very well be incredibly happy single or meet someone else who loves you and who you love and be incredibly happy with them. Either is better than slowly dying in your current 'marriage'.