Subject of this work is especially philosophic approach to the nature of marriage and adultery. Even though the definition of marriage as monogamous heterosexual relationship wove in the foundation of western civilization in the last period of time are even more present requests for redefining the mere concept of marriage, but also moral and legal status of marriage so that marriage does not represent anymore the only social and moral framework of human sexuality. Within some theories about the nature of sexuality (procreational theory and theory that connects sexuality with love) marriage is mandatory or at least advisable framework of human sexuality, while conventional theories interpret marriage as basic institution of society that ensures its stability. Even though for many apologists of traditional attitudes and conventional norms monogamy is natural, normal and moral, it cannot obtain consensus because many predicate that monogamy is not innate and does not satisfy modern people needs. I hold that choosing monogamy is personal because every person chooses according to his/her preferences and beliefs. Appropriate moral judgement for moral status evaluation of extramarital sexual relations and especially adultery, can be brought by implementing moral particularity. Moral particularity attitude is most suitable to the attitude that I defend: because of social and cultural differencies in reference to marriage and adultery, absence of unique marriage definition and adultery as also differencies of philosophic approaches to the nature of sexuality, each adultery has to be examined for itself. Everything else is less appropriate and rough theoretical tool for moral judgements. Therefore I defend attitude that I represent; i.e. in adultery is possible to find conditions that make it morally justified. As far as regards moral justification of adultery there is a fact that one or both partners avoided the content of promises given or understood in marriage vows and one of the partner submitted request for termination of marriage while the other partner did not accept that request. Notwithstanding which marriage vows partners obliged themselves, violation of the same on behalf of any of the partner opens possibility to be free of his/her moral obligation. Nevertheless it is sure that moral behaviour obliges partners not to do anything that could disturb confidence and respect of the other. It seems to me that it is very important to underline that in cases where there is no love anymore is preferable moral option of honesty towards partner than adultery. Love is complex phenomenon that is also in a complex way connected to sexuality. Many hold that adultery happens only to those couples that are in love crisis and never to couples that are in satisfying love relationship. I think that this is basically wrong attitude. Love is independent of our will. However we can influence to be or not to be with loving person. It can be hard but is possible. Adultery, according to that, cannot automatically be justified by falling in love with partner with whom we are not married, as also one should not be judged or justified because he/she is not in love with partner with whome he/she commited adultery. It seems that love and adultery are not connected in a way it is presumed. Relation emotion and sexuality is far more complex than it is considered usually. I hope that I succeeded to demonstrate that there are many circumstances intrinsically different from traditional prejudices and conventional moral norms when it is about institution of marriage and adultery.