What will you do if one day you find out that the man of your life has a kid with another lady?

one day i looked in to my mail and i found a letter from the dep. of child support, with a huge curiosity and with some nerves i opened the letter and there whas this lady alleged child support to my husband , my husband explained everything and feel really bad i dont know what to do, i cried all day im really deppresed....