Gemara

(Beraisa): If he had borrowed things that she received from her father, she makes a Shali'ach to receive payment.

(Rav Sheshes): If they come to Beis Din together, we do not accept their case.

(Rav Papa): We excommunicate them.

(Rav Huna brei d'Rav Yehoshua): We (also - some texts omit this word) lash them.

(Rav Nachman): This applies to divorce from Nisu'in. If he divorced her from Eirusin he may pay her directly, since they are not intimate with each other.

A couple divorced from Eirusin came in front of Rava.

Version #1: Rava set up a middleman so they should not deal with each other.

Rav Ada bar Masna: Rav Nachman taught... !

Rava: I saw that they are intimate with each other.

Version #2: Rava did not set up a middleman.

Rav Ada bar Masna: Set up a middleman!

Rava: But Rav Nachman taught... !

Rav Ada: That is when they are not intimate with each other. Here, we see that they are intimate.

Rishonim

Rif and Rosh (2:33): If he had borrowed things that she received from her father, she makes a Shali'ach to receive payment. If they come to Beis Din together, we do not accept their case. We excommunicate them and lash them. This applies to divorce from Nisu'in, for then she recognizes his winking and gestures. If he divorced her from Eirusin he may pay her directly, unless we see that they are intimate with each other.

Ran (DH Mi): It seems that the Isur to claim directly from him does not apply to a Yisrael's wife before remarrying, for she claims in Beis Din and there is no seclusion. However, perhaps we are more stringent because they claim from and talk to each other.

Ran (DH Rav): Rav Huna says that we also lash. The latter opinions come to add, and excommunication is harsher than lashes. Alternatively, we only lash. People consider this to be more severe.

Rambam (Hilchos Isurei Bi'ah 21:27): If a man owed his ex-wife, she makes a Shali'ach to receive payment. If they come to Beis Din together, we excommunicate them or lash them. This applies to divorce from Nisu'in. If he divorced her from Eirusin she may claim from him directly and live with him, unless they are intimate with each other.

Magid Mishneh: The Rambam says that we excommunicate or lash if they come to Beis Din together because the Gemara did not rule like either opinion. Rashi says that we discuss a Kohen. The Gemara does not suggest this.

Beis Yosef (EH 119 DH veha'Rambam): The Rambam was unsure whom the Halachah follows, so he lets Beis Din decide. He holds that we discuss a Yisrael's ex-wife even before she remarried.

Poskim

Shulchan Aruch (EH 119:8): If he owed to her money, she makes a Shali'ach to receive payment.

Chelkas Mechokek (23): The same applies to other claims of either against the other. All the more so they may not speak in the market.

Taz (18): It seems that this is only if he may not remarry her. However, the Rambam always requires a Shali'ach.

Rema: Particularly in this case (a Shali'ach is required), but he may enter her house even though she remarried, since he does not live there and interact with her. Some are stringent.

Terumas ha'Deshen (243): A man may spend time in the house of his ex-wife and her new husband when the houses are far apart in a small city with no other Yisraelim. We learn from Pesachim 110b. Ploni used to drink in the store of a grocer who married Ploni's ex-wife. The Gemara says that she was able to harm Ploni through witchcraft because he drank Zugos (an even number of cups). If he was forbidden to enter, perhaps this was the cause!

Chelkas Mechokek (24): I don't understand the stringent opinion. The proof to be lenient is sound.

Taz (19) The Beis Yosef (DH uvi'Terumas) did not accept this proof. Also I do not. Ploni transgressed. He was not harmed until the day he drank Zugos! Even if others are present, they do not understand his gestures. Others are present in Beis Din, yet she may not claim directly from him! If Reuven owns a pit in Shimon's house, Shimon makes a key lest Reuven come to take when Shimon is away, causing suspicion that he enters to be with Shimon's wife (Bava Basra 99b). All the more so we are concerned about a divorcee!

Rema: One may feed his ex-wife. It is a Mitzvah to feed her more than other poor people, as long as it is through a Shali'ach and not directly.

Chelkas Mechokek (25): A Medrash (Bereishis Rabah 33) says that once rain came to the world because a man gave Tzedakah to his ex-wife. It seems that he himself gave to her, and that this is permitted.

Gra (22): Vayikra Rabah (34:14) says that "Umi'Besarcha Al Tis'alem" alludes to supporting one's ex-wife.

Shulchan Aruch (9): If a man and his ex-wife come to Beis Din together, we excommunicate them or lash them mid'Rabanan.

Beis Shmuel (17): According to the Rambam, this applies even to a Yisrael's ex-wife who is single. We excommunicate also for living in the same Chatzer.

Beis Yosef (DH u'Vasar): The Tur says that we excommunicate them. He rules like Rav Papa. Alternatively, he explains like Tosfos, that Rav Huna holds that we also lash them. Since all agree that that we excommunicate them, the Tur rules like this. He did not say that we lash them, for it is not clear whether or not the Halachah follows Rav Huna.

Question: In Siman 6 the Tur said that we lash a Kohen!

Answer #1 Beis Yosef (ibid.): Perhaps he holds that Rav Huna holds that we only lash them. He is lenient about a Kohen to lash, since the Lav is Einah Shavah b'Chol (does not apply to everyone). He is stringent about Machazir Gerushaso to excommunicate, for this Lav is Shavah b'Chol.

Answer #2 (Bach DH u'Mah she'Chosav): The Tur explains that Rav Papa and Rav Huna said different laws. They do not argue. The Beraisa discusses married and single divorcees. When she is single, we lash due to 'Lo Tovah ha'Shemu'ah'. If she is married we do not lash her, lest this cast doubt about the legitimacy of her children. Perhaps this is the intent of the Rambam, who said ' we lash or excommunicate.'

Taz (20): The Tur says that we lash a Kohen, for he is lashed for Bi'as Zenus with a divorcee. A Machazir Gerushaso is not lashed for Bi'as Zenus.

Shulchan Aruch (10): If he divorced her from Eirusin she may claim from him directly and live (some texts - be judged) with him. If he is intimate with her, even from Eirusin this is forbidden.

Beis Yosef (DH Kasuv): The Rashba (1:209) was asked if a Yevamah may live in her Yavam's house and eat on his table after Chalitzah. In the case they were intimate with each other. She was the Yavam's niece, and ate with him in her husband's lifetime. He said that this is like an Arus and Arusah who are intimate, even though one could distinguish.

Ra'anach (91): We did not decree about a Chalutzah. This is not because the Isur is lenient. We decreed about one who married a nursing woman and was forced to divorce her, even though all agree that it is mid'Rabanan! Rather, they were never married, so she does not recognize his gestures.