I sympathize with all parties here. There is obviously a problem in the marriage if that person is meeting other people for sexual relations.
All parties here may not be aware of the situation. Everyone is kept in the dark!
Who is to blame? Is there blame? or is it a mixture of miscommunication, growing apart, maybe not enough time with your partner?
The person who initiates the affair needs to be honest with themselves!!!
What do other people think?????