in my opinion there is no excuse for any sort of cheating be it emotional or physical and once that trust is broken-its almost impossible to get it back.
i think during times of stress-people show their true colors. their either your rock or they bail and seek attention elsewhere. i have a no tolerance policy for people who take the easy way out or who need an escape from reality.
when the shit hits the fan-thats when you see how much inner strenght and emotional maturity and integrity a person has.. her blaming your health issues and your whining is not an excuse for her behaviour. if she was unhappy-she could have walked out the door. shes not chained to the bed or anywhere else.
its your decision wether you want to stay or go. good luck to you.