We checked back with Alex yesterday, a little over 4 months after that call originally aired.
Alex and Linda have separated. Alex told us that Linda confessed that David was NOT her step brother but indeed someone that she has been having an affair with. She's always had the "half brother" story in the back of her mind, just in case Alex became suppositions.
All Alex could repeat to us when we checked up on him is, "Man I'm glad I decided to wait to have kids with her".