Relationship problem..HELP!!!!!!!!!!!?

Ok i jus told mii boyfriend that we should jus be friends. why? becuz he lies and he cheats.. he think i dnt kno but i kno more than enuff. mii friend called his phone block and asked him did he have a girfreind he said no and that he hasn't found the one. but he has told me that he is fallen in love with me. and the other day we was at the park and this girl was there he playin with her and err thing =(. he told me that she is like a sis but look she put hickies on his neck and mii friends sister told me that they use to go together. now that i tell him i want to jus be friends he's cursin and sayin i shouldn't believe wat ppl say.. What should i tell this cheatin no good dude??