That's the thing about love. It's a feeling that can't be described by anything other than the word love. But it's not set in stone. Just because she said it before does not mean she feels it now. You made a blunder, you screwed up, and you broke your trust in her. So she doesn't feel it anymore. Our feelings, our thoughts, our minds change all the time. What you did really hurt her and broke her heart and her love for you hurts. It makes her angry that she could feel that way about somebody that could do that to her. While as far as my understanding is that you didn't sleep with this girl, your ex doesn't know what to believe and assumed the worst. I guess you could try and explain your side but if she's not talking to you and not listening to you, there isn't much you can really do about that.
Learn from this experience: do not let your jealousy turn to trying to control her, and think things through when involving other girls before you make mistakes like this again. Like drinking with a girl that seems interested in me when I have a girl I'm in love with already: is it worth it? What am I trying to get out of it? And then you can remove yourself from the situation before more damage occurs.
Waking up next to a beautiful girl,
Step outside and say hello to my beautiful world.