Siman 615

Yom Kippur is forbidden for tashmish hamitah, and this too is included in "and you shall afflict yourselves," for the withholding of tashmish is called "affliction." And in the Gemara (77b) this is derived from a verse, see there. And even in a place where they do not immerse for keri—tashmish is forbidden (Tur), that is to say: so that you should not say that the prohibition is because of the immersion that follows, due to the prohibition of washing, but rather the tashmish itself is forbidden. Therefore, a man should distance himself from his wife all this day as if she were a niddah. And that is: that he should not sleep with her in one bed, and he should not touch her at night. But during the day there is no concern, of course (Taz). And there is one who forbids even during the day (Magen Avraham), and it seems that the custom is not so. And he should not speak extensively with her (ibid.).

We learn at the end of Yoma (88a): The school of Rabbi Ishmael taught: One who sees a keri on Yom Kippur should worry the entire year. And if the year passed for him, he is assured that he is a son of the World to Come. This is the wording of the Tur: He should worry, etc. — for they are showing him that his fast was not accepted, and they satiated him with that which he has the power to be satiated. Like a servant who pours a cup for his master, and he spills the pitcher in his face. And if the year passed for him, he is assured that he is a son of the World to Come, for he certainly has merits that protected him. Thus far his words. Rashi and Tosafot wrote: And a sign for the matter is "He shall see seed, he shall prolong days," and so wrote the Tur. (And I heard according to what is written in Shabbat 105b: "All the days of the elders who prolonged days" etc. — they prolonged days, they did not prolong years. And it asks: If so, "In order that your days shall increase"? And it answers: A blessing is different, see there. And this is it: if the year does not pass for him — "He shall see seed, he shall prolong days," but not years. And if the year passed for him — it is a blessing, and he shall prolong days and years.)