This is one of the saddest threads I've read on Mumsnet for a while.
You get one precious life - and you can't just give up on it in order to be a good parent - because that will not, and has never been a way, to make children happy and secure.
Branflakes - you say you can't face the thought of leaving because you dont believe there is any better option - it sounds as though the pain you have been through in life, for many reasons, has left you unable to believe that you could actually have happiness.
Your marriage does not sound dull it sounds unhappy - your partner is actively making you feel worse about life - have you considered that without him around a weight might actually be lifted from your shoulders? Your children are learning, subconsciously, how to have relationships by watching you - and I can't believe that a marriage where he doesn't help or support you - and where you can't talk to him openly - are teaching them to have good relationships.
Most of the people who come onto Mumsnet to talk about problematic relationships are living out patterns they learnt as children - would you want the life you have now for your children, or do you hope for something more? They need to see you choose life - to choose happiness as a possibility.
Isn't it better to set off down the path to try and find a better life, than to stay in this situation - where you are numb? People here who say that 90 per cent of long marriages are mundane - I simply don't agree. Relationships are part of life, so if you have an interesting life that makes you happy, your relationship will reflect that. if you find your life mundane (rather than calm or temporarily uneventful) - doesn't it means you believe in your heart there is something more?
Even after 30/40 years, you can still begin new projects/ dreams/ work/ learning/ meeting new friends - how long your relationship has lasted has no bearing on that. And that in itself will revitalise your relationship.
I agree with the posters who said, you should be looking forward to the years ahead, to the plans you have together. Essentially - your partner should make you feel better about life, not worse, at the very least.
The BACP website will have a counsellor near you - I really think you would benefit from talking to someone about why you are afraid of being on your own rather than with someone you dont respect or love. You dont need to meet someone else - not at first anyway - sorting our your own life will be the first challenge - make a plan for the next 12 months - places to see , friends to make, some gentle ambitions to achieve... - you are YOUNG woman! get a grip and do not give up on life .....there is so much possibility ahead of you.
If not for you (at first) then start by thinking of being a role model for your children - they need to see you seize your own happiness so that they can learn to do it too.