bertieb, I understand how you feel. It's really hard to not entertain the feeling of guilt, I had been there. I felt so bad when I can't or not able to help specially financially but I felt terribly worst when I realized I was used. Someone advised me these:
-the giver has to set the limits because the taker doesn't have limits
-you can only do so much (you can't do everything)

save your money for your kids, they deserve it!