Sorry it happened to you. Its good to forgive people but dishonesty now is a bad sign for the future, no matter how much maturity has occurred in a year. Still you gotta follow your heart as they say, often that means more hurt but sometimes more hurt is worth the positives.
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Preachy portion ( continue at own risk, have no idea if this applies to any of your situation):
I think part of the problem people run into today is that they do not follow traditional relationship norms or even have much in the way of boundaries in the whole dating world. Often we treat relationships like "mini-marriages", where is not only sex a given but monogamy is assumed. They are not marriages at all.
I wonder if relationships at that stage should assume non-monagamy instead, and it should be talked out explicitly whether the participants are going to actually have sex with other people. Not simply " see other people"that is too ambiguous of a term. (not saying you didn't do this, i think most people do not)
You get this serial relationship problem that so many people deal with in their 20s, one bad thing to the next, exasperated be the fact that people are having sex which clouds the relationship and is like coating problem food with a thin candy shell.
Every relationship should have clearly discussed boundaries. In general, people attempt monogamy when they are not prepared for the commitment. Heck many marriages have no business with this boundary unless people are prepared for it and really want it.
Another option is just to date but not worry about the monogamy thing. A little conquering of the jealousy dragon is probably not a bad thing for our maturity.
Finally, there is nothing wrong with waiting on intimacy until the commitment is there, marriage or whatever. People will have better relationships by getting to know the person without the pressure (and yes even with the benefits) of all the other stuff.