OP I hope you are still with us.
Please listen, your children have started school, but in fact this can be a period of time where you can support them - especially with SEN it can all the difference to outcomes. I would see it as a godsend that you have the option and time to support them fully.
In the day time I would use the time to choose a future career you feel very passionate about, and study (very) part time to achieve the qualifications you need. You will make new friends on the course, it will give you a career that truly means something to you when the time is right and you can reenter the work force (if you want to) and you have a plan B should your marriage struggles later in life. Ensuring you have financial security for your entire life, even post children is absolutely essential.
When you are not studying:
Book a spa day or massage
Look after your feet, nails, skin and hair with various appointments
Put together photo albums and memory books for your children
Redesign your house and garden
Make new or see old friends for lunch and coffee
Yoga and meditation classes will do wonders for you balance
Rest, so you have plenty of energy for your children when they are at home
Once a month help with the foodbank supermarket collections
Write a book
In a few weeks you will come to love your time at home, that is tidy and calm peace. You will treat yourself to an afternoon in bed reading or watching a film you longed to see, the break from life that many of us are so in need of.
You have been 247 for years and years, it is adjustment that is all. You will get used to it and wonder how you managed lying solo with no respite for so long!