Is it bad to walk away?!?

okay.... well my boyfriend william use to hag out with this girl name tania he told her every thing.. one day i thought i was pregnant and he told her. and i told him not to tell any body.. #2 he tol me he doesn't take pictures with any body but i was using his Phone and he had pictures of tania ad him together... and i told not to talk to her and hen he said he promise he wouldn't and then the next day e rends came up to me an said that they were sitting on the bleachers talking all period of p.e.. so then i confront him about it he said he didn't take me serious. so then i was taking about her and he called me her name twice i can understand the first time because we were talking about her but then 5 minutes later we were kissing i get up to get a drink of water and he says tania come back.. the he had anther girl name vanessa n his back and he admitted that he kissed her hair.. and then i found anther picture of her in his phone yesterday. and i know i've done my fault but then he trays to get me mad a purpose he got mad at me because i didn't want have sex... so the like he says stupid crap like oh you don't care about me you still have feelings about other people when he knows damn right that we've been threw allot and he should trust me.. and so when he says stupid **** ;ike i don't want to de all with the fighting because we do it all the time so i walk away... and then he tells me not to do something i don't do it then he gets mad at me later for not doing what should i do im confused