That is very difficult. Men are raped by women and they do keep silent, however, as with any rape case the longer a person takes to report it, the more difficult, if not impossible it becomes to prosecute it, which is especially true for adults.
As for the child support aspect, if it's his child then yes, he is obligated to pay child support, which is the right of the child, not the parent. The child didn't do anything wrong, no matter how it came to be.
If you fall down 10 times, Stand up 11.