I feel like i ruined everything, how do i fix it? :[?

last night at a party my bf was no where in sight theni seem him walking fom the dark with another girl...i automatically assumed and i didn't go up and talk to him the rest of the night i was so hurt...he came to say goodbye to me and i was really quiet with him and hesitate.....and he seemed like nothing was wrong...later he texted me sayiing he missed me...then i just had to bring it up i was sick to my stomach...i said i miss you to but you made me nervous tnight and he said why? you did seem wierd. and then i explained and he said "that was rachel i went to get beer with her...i went twice..nothing happened" and i automatically felt dumb...i knew he didn't do anything soi apologized...but he got soo mad at me and he still is he doesn't like the fact that i didn't trust him i don't know what to say or do : ( last nightt he didn't want to talk to me anymore and this morning he texted me "sorry if i mislead you i wouldn't hurt you. you should know better" and then i texted back saying i was sorry and that it wasn't his problem its mine and he didn't deserve for me to be like that to him and i would be angry too, i understand why he would be mad or hurt cus i would to...and he hasn't said anything back : / i know i was in the wrong i know i jst need advice on how to make it right again...how can i prove to him that i do trust him? i do now i got my reasurrance..