I agree with Time, that validating her possible thought about someone else is not wise.
Validation is a tool of communication and lets face most of us find ourselves here because soemehere the communication broke down in the marriage, or realtionship.
Learning to validate, promotes empathy, and you can use it mostly on emotions or thoughts. i.e. "I feel like we don't fit", "I think I hate you."
Validating actions can be done, but its trickier. i.e. "I slept with your boss last night."
I do agree Pin that not everything can be validated, but in a realtionship where two people are part of the problem, most of it can be.
Experience is a brutal teacher, but you learn. My God, do you learn. - C.S. Lewis
Life is usually all about how you handle Plan B. - Jack3Beans
Listen without defending; Speak without offending - FaithinAK