A Mutual friend said my man had cheated on me but yet after all the heartache she isn't calling to see how I a?

doing....My boyfriend and I had a fall out on sunday nothing to do with women just our differences so i kept my distance..then days later a mutual friend of ours told me that he said"out of all the bitches I am his main "..I'm like hold up back track that I said what u mean he cheating on me..she said Yes ..Yes he is cheating on u...im hysterical..crying ..I call him and he said it's not true and how he don't have time to hear the emotion....he called her..I talk 2 her on the phone and tell her to pick his call up 2 see what he had to say..far as I know they suppose to had been yelling back and forth at eachother ..it was too long for me..i kept constantly calling none of them is answering my call...their reason because they were cussing eachother out...he calling me like a maniac now.....and when I need her the most she is is hardly calling me..I call her .I got to a point yesterday I came home from work and grew sick of the heartache..he told me two small lies b4 so now I'm not sure who telling the truth...I know for a fact she is a scorn woman that is currently cheating on her man because she is hurt from her previous man..my man I don't even know what to call him was persistant with trying to see me after almost a week..he keep calling but I keep pushing away because I don't know what to believe and this friend of mine is not supporting me at all...should I give him a chance and leave her alone?