No one EVER deserves to be cheated on. It should not be accepted, and you should not blame yourself and say " OK I UNDERSTAND" and you should NEVER thank her for doing this, it is damaging, and allthough you might have done wrong and not give her the attention she feels she deserves, the fact that she slept with another man, in your home, is just way out of line.

you both need to get into couceling and figure out what is going on here. you did not make her do it, she chose to lay in another mans arms.