Advice needed. Please be kind.

Hello everyone. So my boyfriend lied to me about going to work a couple of days ago, and we argued about it but we worked it out and forgave him. Well last night I came to the realization that he had me blocked on snap, but he forgot to block my baby brother. He cheated on me last night and posted it. So I'm very pissed and hurt, and I cuss him out. He proceeds to tell me it's MY fault he lied to me bc he tried to be with me, and that the cheating and everything is my fault. He said I shouldn't be upset and that I'm nuts bc I'm sad. Idk how to feel better or what to do.. Please help