Because I have just reached my limit.
Long marriage this sums it up perfectly and today I have had enough.
Not sure why I am posting really, my ducks are in a row (as of last autumn), he will leave our home to focus on his career which has become an obsession, he works every morning noon and night, seven days a week (academic). The only time he isn't working is devoted to cycling or swimming.
We are a permanent inconvenience, even watching a family film involves him working on his laptop. Dinner out involves him writing down things that come into his head and getting short if he is interrupted.
Any conversation involves him staring into space thinking about his work.
I will be able to manage financially, just about, unless he wants half of the deposit (which was a gift from my parents), then we will need to move house.
I have tried so hard, I have spent years making allowances but have reached the end of the line. Even though I know it is the right thing for me and DC I am sad.
I haven't told anyone yet, nothing has changed really apart from me recognising that he will never be who I want him to be.
I am independent financially and socially - have worked hard for that over the last three years after giving my career up when DC were small.
He can't be bothered to make any effort socially, no one is interesting enough apart from one of my friends. He develops an interest in everything I do, i.e. wants to piggy back onto it which is stifling.
DC won't be surprised, they prefer it when he isn't here 
and actually say things like 'we love it mum when dad is away, everything is so calm and happy'.
Definitely the right thing but still.