When a H goes for a chick much younger than they are it is b/c these "college age girls" are always telling them how wonderful they are!! That is why- it's not love at all.... It is how these girls make them feel "special, important, sexy, intelligent"
So don't think for one minute your H is in love with this girl. This A will end eventually! I worry more about my H's A b/c his GF of 2+ years is actually older than him! They have things in common and are on the same intelligectual level if you know what I mean! These young girls don't have a clue, but these MLCer's love the attention they get when they are with them.
To fight fire with fire-- be kind and interested in your H's life whenever you get the chance to see him. Don't go overboard with the kindness, but don't be nasty either. Let your H see you in a "new light". And don't forget you have your children, this is a bond you and your H will have for the rest of your lives. Your H won't have this with his GF, not unless they want to have kids together-- hopefully not! Huge age difference - she will probably grow tired of your H very soon!