i stayed (as did she, later).
we're better than ever 10+ years after.
we met when we were 17, she had an incredibly distorted view of what an adult relationship should look and feel like (thanks PILs), and was incredibly damaged by the model she had, desperate for the validation she never felt she got from MIL (and the validation from me didn't count, as i was "supposed" to love her).
we stayed together for the children initially, then i had an EA. not for revenge, but an extremely immature and selfish response to feeling i deserved some of the love and support i'd always worked hard to give her.
after that, we both talked about what we wanted for our futures, and both agreed that we still loved each other. we committed together to make our marriage the best it could be, and to give our DCs a healthy example to follow. this has worked very well for us so far!
i'm conscious that our DCs are getting older, and i understand it's possible once they all fly the nest things may be different, but at present we're still happy with our choices, and remain actively committed to them.
she has done a huge amount of work on herself, and has changed so much from the person she was in her 20s. she has much higher self-worth as a result of her career, and other activities she's involved in, so is no longer so desperate for validation from MIL.
if things don't work out for us longer term, i'm happy with the choices i've made, and will have no regrets.