Plz help me solve the biggest mistake in my life

well i met this guy that i honestly likt alot and i have been going out with him for like 7 days , my best mate is going out with his best mate , its like three girlfriends, me and the other two girls , so wut happened is that one day me and one of the girls , the third one who is single , went out with my boyfirend and his best mate who a ctuallt is one of us , the three girld boyfriens but his gf , whos also my friend didnt come , we spent the day me and me bf wut i noticed is a spark between my girl friend and my botfriends mate which is wrong becoz hes going out with our best friend , how ever on our way home me bf had to go somewhere and thier was the three of us me my girlfriend and my other girldfriends boybfird so wut happened is that the two of them kissed and they didnt want me to tell theother girl , his gf, that they did so to make sure they made me kiss him as well , sothey make sure i dont say nothing , they said i will be the one who snitches and stuff, so the next day i heared from my friend that that guy told my bf he kissed me and now my bf is really upset and i dont kno ow to explain , i swear i didnt want to kiss him i dont even like the boy,plzzzz am begging u to tell me wut to do am sooo upset and feeling bad ,i feel lke abitch to hurt my bf but i didnt ever cheat ona bf and i will never will, as i said ididnt wanna kiss him he jus pulled me and it jus happened ifelt as if i had to do it coz i was an alen between them two plz tell me , did i do wrong , wut cn i say to my bf to forgive me and mkae him understand