should I get back with him?

me and cassidy got toghtr in april dis year (form4).I didnt knw he existed in form1 and only noticed him at the end of form2. we became frens in form3. aroun july form 3 he told me he was in love with me. he said that hes been in love with me since form1. amazingly I fell for him. but if refused to admit it. thr was sum things goin on betwn us durin july&august form 3. but then durin christmas we had a huge fight. in jan & feb of form 4 I refused to talk to him at all. he tried so many times but I pushed him away. but then finally we got toghtr the 1st week of april. we only lasted a week! den he askd again,dis time we lasted 5 days! den in the end we decided to be in an open relationshp. it worked we lasted 3 month. I just dump him 3 weeks ago. but I coudnt get him out of the system and apparently same goes to him. he just asked me back yesterday. shud I say yes? I mean I love him and he loves me. and I knw hes not lying because I trust him. the thing is that he doesnt trust me.