There are all kinds of meanings to an affair. It can be sexual but it doesn't have to be. I corresponded with a 'brother' on another board two yrs ago and he was married. It started as purely innocent friends and I didn't even realize it but he was falling for me. He was using me as a shoulder because he was having a lot of problems with his wife who refused to be 'part of his life' but yet cried to the elders about everything little thing. I would listen when he needed to vent. What I didn't realize was that he actually even thought of leaving his wife and getting in his car and coming to see me and not just to talk. In my eyes in a way, that was close to an affair, even though I had no idea he was developing feelings for me. We had to stop talking to each other when the truth came out because it wasn't a healthy thing for him.
As far as online affairs in a sexual way, I guess in a way what I am in now started there. Although my soon to be ex had left the house, my divorce still has not gone through. but when he left, I let myself be open to meeting some people online, first just in chat (such as yahoo) and some of them lead to meeting in person.. One of those men found his way past the flirtatious fun into my heart and now shares my life in every intimate way. Is it an affair? I guess, since technically I am still married, even if I refuse to consider what it was a marriage..