Fostering children can be an extremely rewarding and fulfilling experience, and it almost always is a very exhausting, emotionally difficult experience. You should NOT foster a child if you are not willing to have your heart broken into a thousand pieces over and over again.
However, if you are prepared for the reality that it will be exhausting, and maddening, and will effect every aspect of your life for an indefinite amount of time, then the foster system could use you. The kids could use you.