why won't my bestfriend(guy) accept that its my fault?

me and bestfriend (guy) along with his friend, we 3 went to my bestfriend's ex gf's friends place and his ex gf planned to go to the gas station to buy some candies quickly and it would be just her, me, my bestfriend and this other girl...my bestfriend told me to not go up to zach..which is his friend and not let him know we're going out but then I accidentally just walked to the tv then he came along after and now the planned was ruined because the 2 guys wants to come and zach wanted to go home already and I feel like its my fault...I didnt stay with my bestfriend while waiting for the girls....so we didnt go anymore.....instead he drop zach home and it was just both of us....as it was just 2 of us in the car alone....we were talking and he sounded mad at his friend lol then I told him its my fault because of what I did and he said to me that "its not your fault and I don't blame you" wooowww lol does guys do this all the time to girls????