I went thru something similar. A couple years ago I caught my wife having phone sex with a guy she met on the internet. It is very soul shattering to hear voicemails from another guy saying he loves your wife. I was furious but eventually we talked. I lost my job and was going thru a bout of depression. Our sex life was suffering and she wanted intemecy. That is why she did it. We eventually worked things out but I still have a hard time trusting she is faithful. If it happened again I would most likely leave her. She never talked to the guy again and things seem to be more good than bad now.