Agree with above. Knowledge is power, and power gives courage.
Work out your finances. Check with a benefits calculator and see if you can get help with childcare or rent at least. Go on CMS to see how much he would have to pay if it wasn't 50/50 (is he likely to want that?).
Look on rightmove to get a rough estimation of your house, then deduct the mortgage owing to find your approximate equity. Find out both pensions. Since everything is online now at the very least find out how many he has and who with as that can help the solicitor. Start separating finances, take your share of any joint savings.
Based on an estimated 50/50 split of house, pensions, savings etc work out if you can afford to buy a smaller house or a rental. Keep adjusting expectations, locations and wants until you find something.
Finally get a one off consultation with a solicitor.
Once you have looked into everything and dreamed of what it could be like, eg no dirty clothes dumped on the floor, no Top Gear or football on the TV, a cleaner or tidier or quieter house, that is when you tell him the marriage is no longer working for you. Good luck.