Need Opinions

My friend opened up to me about being in this sex relationship that's what i call it. She met this guy on a talking app. At first they got to know each other and soon found out he was married and had two kids. She didn't like the idea to much but they soon got sexual. After going on for a few weeks on this app they moved to Skype. She said things hit it off great he was sending nudes. And it went on even longer. She soon after video chatting on there got attached to him. It was a mess and he felt attached to her. But he always told her he wasn't leaving his wife. So what I was thinking is this is all about some sexual attention. He goes out of town for work and stays in hotels and hits her up. He has sent nudes, videos and they foreplay over text aka sexting. I don't see why she does this it isn't fair to her like she gets attached and it leaves her slumped.