Yitzchak Coffer asked:
I can't understand how Rashi allows a man to aser on himslf pleasure when at the same time he is obligated in Onah. How can he fulfill the latter without the former?
Yitzchak Coffer, Thornhill, Canada
The Kollel replies:
True, he will be unable to fulfill his obligation and he will have to divorce his wife. However, as long as the Neder is not made directly against his obligation, the Neder is valid. After the Neder takes effect, the Isur caused by the Neder prevents the fulfillment of his obligation. The Neder itself is only invalidated when it directly opposes the obligation itself (i.e. "the Hana'ah of my Tashmish should be Asur on you").
Dov Zupnik