You should think of it this way....How would you feel if your husband was having an "emotional affair" with someone...? Let the man dig his own hole, but dont be the one that helps him...He got married for a reason, so atleast let him get divorced before you start anything with him...
Oh and what makes you think that a year down the road, he wont be having an "emotional affair" with someone else....if you do it once, 9 times out of ten you will do it again....hope this helped you out in some kind of way