My heart hurts

So I just found out my boyfriend has been sleeping with his ex. He broke up with me a week ago because I was having trust issues because I seen she was texting & calling his phone all hours of the night.. He started ignoring my calls & started being more distant & when I confronted him he broke up with me & for the life of me I just couldn't understand why it was so easy for him to just walk away from our relationship after we talked about marriage & kids & the whole 9 yards..The Ex Even went as far as messaging me on Facebook saying "she's not the crazy ex for nothing".. I wanted to know so bad what she meant but I told myself not to feed into her bullsh*t.. Come to find out my insecurities were right all along..I'm so hurt because I love him so much.. But I can't believe he couldn't just be honest with me & tell me the truth.. I'd rather know the truth then to live a lie.. & most men don't realize they can do more damage with a lie then to just tell the truth..