Another Girl Kiss My Boyfriend...?

Everything was pretty much normal yesterday he rang me at the normal time we talked for a couple of hours he did seem a bit down but he just said he had a bad day with some mates as you do. But then i got this txt this morning saying "...im so sorry... " i wasn't to sure what he meant so i just waited for something to come after that ... and it did it said ; " I fukd up... yesterday.. Whn i was wth all my mates. Rose tryd 2 Kiss me..N b4 i stpd hr she was alredy done :'( i swea i neva wantd 2 she cme on 2 fst " ... Well as you could imagine i was pretty upset i wasn't to sure what to say back to that so i just said "Ohhh.." he keeped saying how sorry he was and how much he loved me. But i was just heartbroken,upset,angry. I just don't know what to Believe i don't know this girl, and i wasn't there. Im Just so confused :( what should i do dump him,talk to him, give him a second chance? everything was going so good ! :-(