There are all kinds of reasons. For some people, it's just an opportunity they couldn't pass up. There is some draw to have some of that excitement and they still want to be in the relationship they are in. For other people, it's a symbol that there are real ongoing difficulties in the relationship. It's not being satisfied and seeking that out elsewhere; whether it's the sexual side of it or an emotional connection. It can be very different. Some people are looking not so much for the sexual part, but just for a deeper emotional connection with someone else, or to be appreciated because the spouse is not doing it.
