Yes, it was David Birney. I believe he said he was guilty but had gone through therapy and was now "cured". He also said he was a therapist himself that was dedicated to helping other child molesters. Towards the end of the episode Nancy walks in on Timmy giving Birney's character a hug and Nancy screams. It's then that Birney's character realizes Nancy will never trust him.

I believe the child molester episode was "Malicious Mischief." I just bought seasons 3 through 5 from www.ioffer.com. The seller had all but two episodes, one of which is "Malicious Mischief." Nancy falls for Timmy's day care provider, then he's accused of child molestation. I don't remember whether he's guilty or not. He was played by Meredith Baxter's then-husband, David Birney.

I was also just a child back when the show originally airedI can't really remember the ex the was the child molesterit DOES sound familiar thoughNancy has A LOT of weird friends thoughbut the one that was addicted to pillsthat's from s2it's on the dvd setit was the guy she was going with and left to marry Jeffhe was a doctoraddicted to Speed I think.