If its purely a mismatched sex drive, then buying yourself a BOB should fix your problem.
But! From what you've written, sounds to me that you actually crave the reassurance sex brings, as opposed to the orgasms...
Distinguishing between which of these two scenarios is the actual issue, will lead you to your solution.
If you're just plain horny all the time, then its time to take some responsibility for your own pleasure. (I'd be singing a different tune if your bf never or hardly ever wanted to have sex) but I digress...
If it's the BDD quick fix you crave, well then it's also time to take responsibility and take this issue to therapy.
Whatever it is, cheating is obviously not the answer. This would be such a senseless way to destroy a good relationship, and would no doubt add to your emotional and mental turmoil.