BND - My son, at 19 also confronted maggot (OW) who was "living" with my ex 2 weeks after we split! She told him they were "in love and wanted to spend the rest of their lives together" - yep 2 months after we celebrated our 25th. Then she tried to take out a restraining order on my son (who is totally non violent) so he would never again disturb their "love nest". What a gem!
Yikes! Sounds like your ex-H and OW deserve each other since they both appear to be absolute jerks. Sorry your son had to experience that craziness!