Assalaamu alaykum. Please do not refer me to other fatwas. Last time, you mentioned other fatwas, and I cannot understand that way. You told me that one is allowed to drink the remaining water of a marriageable person. How could this be allowed in Islam; is drinking the remaining water of one who has placed their lips on the glass permissible for another person? Is one allowed to drink from the same glass as their cousin of the opposite sex who drank from it without washing it? I know a hadith but do not remember its reference: it goes something like:
Whoever drinks from the same glass as a marriageable person; one must not drink from the same glass without washing it because drinking from that same glass produces love between the two persons.
Apart from that, there is a hadith that says something like:
The husband and wife drink milk from the same glass on their first wedding night.
Is it true that drinking from the same glass causes love between people?

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. 

The rule that was established by the jurists is that all things are permissible in principle. So it is not permissible to issue a ruling that something is forbidden except with evidence.

Abu Tha’labah Al-Khushani narrated that the Prophet said, “Allaah has ordained obligations, so do not abandon them, and He has set limits, so do not exceed them, and He has prohibited (certain) things, so do not violate them, and He has left (certain) things (unmentioned) out of mercy to you, and not out of forgetfulness, so do not pursue them.” [At-Tabaraani, Ad-Daaraqutni and al-Bayhaqi]

On the other hand, we are not aware of any evidence or statement of the scholars that prohibits drinking from the same place from which a non-Mahram (marriageable person) drank, nor drinking from the remainder of the water from which he has drunk. Also, we have not come across any hadeeth with the meaning that you have mentioned.

Yes, if someone intends sexual pleasure by doing so, then he is forbidden from doing it, not because the act is forbidden in principle but because of this (evil) intention.

As the jurists stated, this is like the prohibition of looking at a female Mahram (an unmarriageable woman) with sexual desire, whereas looking at her is permissible in principle.

Ibn Taymiyyah said, “The scholars also agreed that it is forbidden to look at non-Mahram women or at Mahram women with desire.”

The hadeeth that you referred to last was reported about the story of the wedding of ‘Aa’ishah with the Prophet  by Ahmad in his Musnad. But we have not come across any scholar who said that drinking from the same cup creates love between the spouses. In terms of having good marital relations, then this may strengthen the affection between the husband and wife; however, this is not restricted to the matter of drinking from the cup; rather, any act of good marital relationship could have this effect.

Allaah knows best.