I don't understand men?
If your in a perfectly good LTR (12 years), clearly still love your partner, have a very affectionate, loving and caring relationship... Whats the need to have an emotional and physical affair? 
Not my personal experience, but a male friend that I work with. The way he talks about his DP he clearly loves her and they have a good relationship, however I know he is having an affair and its not just for the sex. He is very emotionally and sexually attached to this other woman. I only know because the OW is my friend and as much as I've tried to make her come to her senses, she loves him so she just wont listen and the thing is I really do think he might love her too.
But it got me thinking... can you really love two people at once? I don't think so but I'd like your opinions.
and also why would a man start an affair when he already has a good relationship which he has no intention of splitting up? I could kind of get my head around if the relationship wasn't very good but from everything I've seen and heard there are a lovely couple. 