I know his children long for a mother in their life
but I want him to want me not only a mother for his children.
I think that you're quite right to be cautious,after all,you want to be loved for who you are.
He and I have been talking on the phone or texting about 5 times a week. He has told me that his children love me and will take nothing less but me for their mother.
From this,it's clear that at least you're friendly with him (being in contact so often.)
Also,the children love you too,which is
REALLY important,and after all,the
Reason you've kept in contact with him. :)
By all means invite him out (in a friendly sort of way!! )