Get out.

You have a right to be happy.
You have been with this man..
you don't say you are married
to him, you don't say you have
any official status towards these
children, so what I get from
your letter you seem to be
a housekeeper with bed priveleges.

You owe no obligation to anyone.

Leave the realtionship, and move
on with your life.

The children have a mother and a
father...you were only a volunteer.