Am I a terrible person?

So I'm 17. Ill be 18 on the 6th and I have a 2 month old son. And I found out that my boyfriend/baby dad of five years has been cheating on me since July. Well last night I for drunk and kissed his best friend and tonight I slept with his cousin... And I feel like a shitty person. He is already with the girl he cheated on me with and she knew about me and our son the whole time... And he wants nothing to do with our son. And told me never to talk to him again.