I know for a fact that my best friends husband is cheating because one of my other friends seen him with a girl and my other friend called me the other day and told me this friend does not know what kind of car the husband drives she asked me if this is what he drove and of course you know the rest getting back on the subject I know if I tell my best friend he will not let her be friends with me and its killing me to not tell her what should I do?