Let him go. Don't try to hold your husband back, let him go. If he feels you and the kids are important he wouldn't have done it. File a divorce and walk out of that relationship. If he comes back, sex will be a torture. Every night he is doing you, your mind will wonder if he did the other lady like that too,h did he suck her breast like that, did he lick her pusssy like that, did he kissed her buttt crack like that,... you won't help wondering ..so just divorce him and live with your dignity and a clear conscience.