Is cheating okay as long as your partner never suspects anything?

If your partner suspects you are cheating, they will suffer moderately. If they find out, they will suffer significantly. However, if they are blissfully unaware, no psychological damage is done. On the other hand, the cheater gets pleasure from having sex with other people. If you manage to keep it a total secret, cheating creates pleasure and doesn't create suffering. Therefore, from a purely utilitarian perspective, cheating could be considered morally correct.