Was what i did "unacceptable?"

During the last two weeks of my year and a half relationship i started developing feelings for another guy. But i never told the one i was dating at the time because i thought it would just be another crush that happens after not seeing the guy for 3 weeks. And i thought id get over it quickly. Not to mention, the boyfriend at the time told me " its fine as long as you look dont order"  So i just hung out with the guy to get to know him, and just to bevome friends. But the more i hung outwith him the happier i was. And so it made me think of the flaws of the relation at the time.  Thus i broke up with the guy.