Though it shall be little help, what your feeling is perfectly normal. She has knocked your emotional compass of track, you are having to deal with it. It is normal to feel angry towards her, she is your wife and has let you down in a way you did not expect and could not imagine (one of the frigthening things with this condition is we discover we just don't know someone we thought we knew really well...). In the initial (I feel like knocking her head off stages...), I found that sport was a great way of handling the anger, the pain and the violence. You need too feel good about yourself and look great, and sport is the best medecine for that. You mention that she went for a 23 year old, so it sounds like she knocked your confidence, get it back with sport, respect yourself, love yourself!
I completely agree that indifference is the opposite of love, and that shall come. It takes time to get there (after 3 years i am still getting there...), its a progressive thing. However, even though you may not feel indifference, you must show indifference. I have, and I can tell you that it works, HPD hate indifference, HPD hate not to be considered. By creating a drama, you shall be playing her game, HPD get off on that, it makes them the centre of their stage. Don't forget, no actors, no show

Lastly, I recommend that you keep away from this young mans family. I did something similar (but the circumstances were different), but managed to stop myself before the heat of the moment caused a big mess. You are riding a huge wave at the moment, and it shall be your self-control that shall save you. Please try to use it.
Take care Musician.