The Muslim is not infallible. Every son of Adam inevitably commits sin and the best of those who sin are those who continually repent, as it says in the hadeeth. But it is possible for the Muslim to live in an Islamic society and adhere to his religion as much as he can, following the words of Allaah (interpretation of the meaning):
His religious commitment is not affected by some sins that he may commit without meaning to, or that he thinks are permissible according to his own ijtihaad and reasoning and the information that he has, or that he asked some scholars about and they gave him a fatwa concerning that but the fatwa was not in accordance with sharee’ah. To sum up, what the Muslim has to do is to keep his duty towards Allaah and fear Him as much as he can, to regard as forbidden that which Allaah has forbidden to him, and to strive to do that which Allaah has enjoined upon him. If he slips or stumbles then he must hasten to repent sincerely.