caught him cheating?

While I was with him (bf) some girl texted him saying " you still with you know who?" I'm guessing he was cheating, then he tried saying it was his bestfriend "crysta" but the contact name was different, cause I know her contact name. Then I ask who changed it and it accidentally slipped out of his mouth and he said she put it her self, so he lied about telling me he hung out with her like a month ago he says ( we've been dating for 4 months) last night he tried to hug me and kiss me and tell me he's not cheating ( it's was our 4 month anniversary), it's morning now and he texted me when he got home honestly I don't know what to do or say, any ideas??