The word cheating has many definitions, one being: to fool.
Often, indviduals cheat themselves of passion, love and commitment. All in the persute of physical gradification. I personally don't hook-up with exes. The gateway to old emotions could be potentially reopened with this act. The past, is the past, for a reason. If good sex couldn't save the relationship before, it darn sure isn't going to change things now.
Good sex with an ex is just that...good sex! I'm quite sure that if you hold out long enough someone will come along that will definitely knock your socks off.