No matter what you think of an open relationship, it is still far better than cheating.
Cheating involves lying and more and more lies to cover the previous lies.
Communication and honesty are the most important parts of any relationship.
Two people who love each other, should be able to talk openly about anything, including fantasies.
Jumping headfirst into an open relationship may not turnout very well, it something that you should ease into.
Like testing the waters before diving in.