Some perspective about "staying for the children"...
(I realise you've never said this explicitly, but it feels like this would be one of the main reasons you might decide to stay)
My DW comes from a situation where her DPs can barely stand each other, but continue to stay together.
My MIL is deeply unhappy and very bitter about her life (though she's adamant that she would never leave).
Both parents have made it very clear to my DW that they've only ever stayed together for her sake, thinking that she would be grateful for their consideration of her happiness and needs above their own.
(She has an older DB, who left home at 16 to escape the situation).
She is far from grateful though - she constantly carries a huge burden of guilt that she is the reason for so much of their unhappiness.
They assumed she was too young to notice the toxicity of the situation, but she was always acutely aware.
As a result of this, her view of families and relationships is irrevocably skewed, and has caused us many problems. She has spent almost her entire life trying to make up for MIL's unhappiness.
If you are truly unhappy (and it sounds like you are), DO NOT shift the responsibility for the situation onto your DCs.
They are not equipped to deal with it, and the likelihood is it will affect them for life.
Show them that they have agency.
Give them a positive, strong role-model that they can (and will) be proud of.