All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
According to our view in Islamweb, the Fatwa is that breastfeeding an adult does not make the relation with him forbidden; this is the view of the majority of the scholars. The Prophet said: "The suckling (that is considered) is only the one that is done for the purpose of feeding from hunger". [Al-Bukhari and Muslim] So if a husband suckles the breasts of his wife, this does not affect their marital relationship. Also, there is no contradiction between our view (which is the most preponderant opinion) and the statement of advising that it is better to avoid it. There is no contradiction between the two statements. Indeed the scholars stated that avoiding the difference of opinion is desirable, as this is safer and better for the person.
However, it should be noted that many Islamic jurisprudence issues are a result of Ijtihaad of the jurists (Ijtihaad is a juristic opinion on matters which are not specified in the Quran or the Sunnah). That is so because sometimes some contradictions could appear in some texts or due to other reasons which the scholars have stated. A scholar who is of the view or acts according to an opinion that he considers to be the closest to the truth, he did well and he will be rewarded Inshaa' Allaah for this, whether he was right or wrong. It is confirmed that the Prophet said: "When a ruler gives a judgement by making Ijtihaad on a given issue and it comes out that he was right, then he gets twice the reward, and if he rules by making Ijtihaad on a given matter and it comes out that he was wrong, he gets one reward." [Al-Bukhari and Muslim] Therefore, there is no need to worry.
Allaah Knows best.