i'd like to say that kids are resilient, but in the case of a parent's suicide, they tend to keep the hurt inside. my cousin's father hung himself on a tree in their front yard. thankfully, my cousin was only a toddler at the time. but even now as an adult, he still wonders about his father and what was so bad in his father's mind that he took his own life.
may i suggest that you get counseling for your son? sometimes, talking with a "stranger" is easier than talking to mommy.
good luck. my heart goes out to you and your son.