That's wonderful! I think disclosing something like that, even to people you trust, is probably the single hardest part of dealing with all of this. Stress wise, it's right up there with making it through your first visit with your therapist.
I agree with Castle that he should resist the temptation to "disclose to everyone" that does indeed come with this. However, there's certainly no harm in telling people he can trust. For myself, I told my wife, both of my pastors, the prayer team at my church, my regular doctor (who is involved with other aspects of my treatment,) a few close friends (two of whom were also molested, it turns out) and, of course, my therapist.
Breaking out of the isolation is key, and I wouldn't be surprised if he has a number of people in his life who would be very supportive if they knew what happened. In any event, congratulations on a milestone for both of you and I hope the momentum continues.
Never worry about "three steps forward and two steps back." Thirty steps forward and twenty back are still ten steps in the right direction.