Once a liar and cheater, always a liar and cheater. What else has he been lying to you and everyone else about?
You don't need to tell her, karma will get him eventually, and you don't need to be involved in his drama.
By the way.....RUN don't walk!
Most of us in the lifestyle have wonderful loving relationships and this is just icing on the cake, cheating and lying is not tolerated...or needed.
And welcome to the board!
Blessings
Mrs. PL