hmm. It's complicated.
I think if my husband is truly in love with the other woman, I'd let him go, coz when 2 people are really in love, there's nothing you can do about it, thou of course, I would be really upset, at the end of the day, he chose to marry me coz he loves me.
But if he go to a prostitute I would never forgive him coz that is only lust.
But I think you and your husband need a lot of work to build up that trust again. It's a 2 way thing and it's difficult... hope you guys can work things out.
or you can try to think like this: "if you feel regret in this merriage, nobody can guarantee what is the result if you merry with other man? even yourself!" 2 people can be together is a "緣份", i quite believe in this theory, or maybe 退一步想, 人總不能十全十美的! if the situation is not REALLY BAD, but you feel not happy or satisfied, let's 認命吧!!