Okay trigger post for me.. need to write something tho...

When I was trying to understand my ex and his new girlfriends behaviour (she pursued him even though he was in a relationship with me) I spoke a lot with my T about how i would never want to be the 'other woman' in a relationship.. that I didn't understand what motivates someone to break up a relationship by offering themselves to some one who is in a relationship.
My T put is in simple words (going on past experience he has had with many many patients)... they were along the lines o,f the person in the relationship (especially a steady happy relationship) seems like a good catch as they have already proven they can sustain a relationship and therefore make a good partner..
Hope this makes some sense as I can't get the words in my head to flow easily into print..
So maybe just by approaching people in relationbships it is because of the 'safer'.. 'steady' nature of them.

Personally my mind would always go back to.. well they cheated to be with me.. so when the next person who pursues them comes along.. the same thing is going to happen.

Cheating is wrong no matter what motivates it... You really should see a professional and talk about what are underlying issues I think.