T., I am concerned about you. Please see a therapist ASAP.
There is no reason for you to be in this much pain. Your husband is telling you, your family is large enough. You are so resentful, you are forgetting, that you have a beautiful family and being able to now really enjoy them as they achieve their goals is a wonderful thing..once they are gone, the next chapter of fun begins! Getting to be newlywed a all over again. Hopefully your husband will retire and then you all continue to enjoy the freedoms of travel, grandchildren....it just gets better and better.
You are reminding me of my neighbor that had 4 children..she loved her children so much, but once they were preteens and teens , she craved a baby.. She was a great mom, but she had issues about not being able to accept, that if she could not have a baby in the house, she could not be happy. She became more and more angry, resentful and depressed...
She ended up with a lot of turmoil in their home... It did not end well, after 2 attempts, she committed suicide. , 2 years later their eldest son also committed suicide. She had really loved him as an infant and toddler, but once he started school, they started having issues .. She did not like that they did not need her for every little thing. This happened with each child as they approached kindergarten.
This not a healthy home life for the children you already have. They need to know, they are enough to fill your heart.