My boyfriend cheated on me,what should i do?

My boyfriend of three months cheated on me with another girl.We met on myspace so its a long distance relationship,but i talk to him everyday.He even told me he loved me,but a few days ago he started acting weird and saying he was fighting with his stepmother.But later then i found out that he asked out a girl on a dare and was lying to me about not having his phone and doing things for her so he could really spend time with that other girl.I went through his messages on myspace and found a conversation they had...It broke my heart,I love him so much i just do not know what to do...Help Me Please :(