What this suggests to me, unfortunately, is that you are so checked out of your relationship that you are likely to cheat again. Even if you promise him never to do so, it doesn't undo the bigger problem which is that you are not committed to him and are curious about other guys to the point of acting on your desires. In my opinion, you and your boyfriend are far too young and inexperienced to stay together forever at this point. My advice would be yes, tell him, and prepare to separate.
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