Why did he do this?? why did he side wif him?

on Friday night I was at a party and I was texting my boyfriend jake and this othe kid chase....me and chase have been boyfriend and girlfriend in the past...chase and me got in a fight...he told mt to f off...f you...called me a w****....s***....b****....and all tis other crap... and so somehow or another my boyfriend found out....at first he was on my side saying he would talk to chase about it...well he did...and guess what?? Chase denied EVERYTHING....then my boyfriend got all mad at me and said you lied to me...I said I ddnt and he hasn't texted me sence...then he textedme from chases phone and said I'm wif chase on this one...and then he texted back a few minites later on his phone...we still boyfriend and girlfriend babe!!! We sre bothe thirteen...why is he acting this way?? Should I dump him?? I still really like him....urgh!!! Wha do I do?? =|