helpppp

so I was with my best friend (guy) gf and two othe girls nd another guy.my best friends gf isn't supposed to be hanging out with the guy that was with us bc he didnt like it and want them to. they all lied to him but thats my best friend and I feel terrible not telling him the truth, but he might obviously bring it up to his gf idk what to do tell him or keep my mouth shut there's a chance he might find out, and he will be mad at me but if ge tells his gf my name might be mentioned and her and I are good friends and that will mess up?? so tell or no