When we got married my Brutal Ex insisted I start using the email address that he created for me through his internet service. For a lot of things I did use it and now that we don't have the service, those emails are lost. Luckily for me, I'm squirrely and used my regular email address for a lot of stuff. Every few weeks I put a search term into that email address and see what pops up. So much stuff that will save my butt in the coming mediation and probably trial.
My advice to all you sweet, summer children is document document document. And then diversify. Keep a detailed diary like you're living in 1845, take document photos and keep them in their own monthly folders to back up the diary.Keep a copy of all that on your computer and on a flash drive and create a private email account and email that all to yourself as it happens. It sounds insane but just do it. Don't ever delete text messages. Add weird ones to your diary and add a screenshot to your photo folder.
I wish I had been more diligent over the years but my naive enthusiasm to be "the best stepmom ever!!!!!" sometimes got the best of me. And by the time that finally wore off, I had already disengaged and didn't care.
I was lucky in some ways. I thought that all my documentation was protecting me from an HCBM. What its really done is protect me from a narcissist who put both of us through the ringer and the red flags became too huge to turn a blind eye to.