Help! The guy I love has fallen in love with my best friend!!

Hi Emeh..I am 24yrld old. I met this  guy and we were all over ourselves.Everything changed when I introduced him to my best friend. He came clean and told me he's in love with my friend. He said I should beg my friend to accept him. I am so much in love with this guy and don't want to let go of him. I can't bear seeing my best friend and this guy together. Pls I need ur advice. Should I let go of this guy or should
I let my friend know of his feelings towards her.