If you're not into your relationship and find yourself thinking about other people more, I say end that relationship. It does no good for you or for your partner.
Of course, you may be polyamorous, in which case you'll need to talk and lay down some ground rules. However, it sounds to me like you're just not that crazy about your current relationship?
Either way, cheating is just really, really disrespectful if you haven't agreed on what is and isn't okay to do with other people.