Here's my story, which is how not to do it.
I was miserably married for 18 years, but clearly brilliant at hiding my misery as everyone thought I was content being married to an arsehole. One of my main reasons for not leaving was I felt guilty hat the children would have to spend time with him without me there to,buffer them. Also money - how would I manage - and knowing how ugly he'd be during the breakup.
So I stayed. And I met a man, he was in a similar situation, and we became friends, then more than friends, and then we started an affair. It was very brief and I slipped up so my husband found out. All hell broke loose, husband was furious and horrible but devastated and wanted to try again. And I had done a bad bad thing, and hurt him, so we spent a miserable two years 'trying' which mostly meant me apologising and doing whatever he wanted because I felt so guilty.
He did try a bit but the basic problems were still there: didn't occur to him to try to understand why I was so unhappy. i fantasised about leaving, then did some more serious research, and one day he saw me browsing rental properties. So he got angry and started lecturing me, and the balance shifted, I just said 'yes, I do want us to divorce, I have tried but it just isn't working'. The breakup was awful - 14 months living in the same house while it sold, kids at GCSEs - but then one day I was free, living my life without him.
so whatever you do don't do what I did and put yourself at risk of deceiving your husband - he doesn't deserve that. Be fair, you know you are miserable, get planning, do your research, and get on with it.