Betrayed

I have been with the same person for almost 3 years.  And today I found out  that he's cheating on me.  And I don't know what to do.  And no friends here.  People who i thought might of been friends never told me even though they knew.  I found out from a girl who knew me and is bffs with the girl he is cheating on me with.  So when she found out I was in the picture she had to tell her bff that she is being cheated on.  That's how I found out.  No one cared to tell me.  I'm so angry and sad. And I have no one to talk to.