What is the reward for spouses treating one another kindly?

I ask Allah to preserve the love and happiness between you,
and to fill the houses of all Muslims with that which has filled your house
of good companionship and kind treatment. I give you many glad tidings of
which our Prophet Muhammad (peace and blessings of Allah be upon him)
spoke when explaining the reward of the wife who is as you described: 

It was narrated from ‘Abd al-Rahman ibn ‘Awf (may Allah be
pleased with him) that the Messenger of Allah (peace and blessings of
Allah be upon him) said:

“If a woman does her five (daily prayers), fasts her month
(Ramadan), guards her chastity and obeys her husband, it will be said to
her: Enter whichever of the gates of Paradise you want.” 

Narrated by Ahmad (1/191). The editors of al-Musnad said: It
is hasan li ghayrihi (hasan because of corroborating evidence). It was
classed as hasan by al-Albani in Saheeh al-Targheeb (1932). 

It was narrated from Anas (may Allah be pleased with him)
that the Prophet (peace and blessings of Allah be upon him) said:

“Shall I not tell you about your men in Paradise?” We said:
Yes, O Messenger of Allah. He said: “The Prophet will be in Paradise, the
Siddeeq will be in Paradise, the man who visits his brother who lives far
away and visits him only for the sake of Allah will be in Paradise. Shall I
not tell you about your women in Paradise?” We said: Yes, O Messenger of
Allah. He said: “The loving and fertile one who, if she gets angry or is
mistreated or her husband gets angry says, ‘Here is my hand in your hand, I
shall not sleep until you are pleased.’” 

Narrated by al-Tabarani in al-Mu’jam al-Awsat
(2/206). It was also narrated from a number of other Sahabah, hence it was
classed as hasan by al-Albani in al-Silsilah al-Saheehah (3380) and
in Saheeh al-Targheeb (1942).  

And it was narrated from Husayn ibn Muhsin (may Allah be
pleased with him) that his paternal aunt went to the Messenger of Allah
(peace and blessings of Allah be upon him) concerning some need and he
met her need, then he said: “Do you have a husband?” She said: Yes. He said:
“How are you with him?” She said: I do what he tells me, except what is
beyond me. He said: “Look at how you are with him, for he is your Paradise
and your Hell.” 

Narrated by Ahmad (4/341). The editors of al-Musnad
said: Its isnad may be understood to be hasan. al-Mundhiri said: A jayyid
(good) isnad. It was classed as saheeh by al-Hakim in al-Mustadrak
(6/383) and al-Albani in Saheeh al-Targheeb (1933). 

Al-Manawi said in Fayd al-Qadeer (3/60): 

i.e., he is the cause of your entering Paradise if he is
pleased with you, and the cause of your entering Hell if he is displeased
with you. So treat him well and do not disobey his commands with regard to
that which is not a sin. End quote. 

As for the glad tidings which came to the husband who treats
his wife kindly, it is when the Prophet (peace and blessings of Allah
be upon him) testified that he had perfect faith which dictated that he
should enter Paradise, and that he is superior to all people. 

It was narrated from Abu Hurayrah (may Allah be pleased with
him) that the Messenger of Allah (peace and blessings of Allaah be
upon him) said:

“The most perfect of the believers in faith is the one who is
best in attitude, and the best of you is the one who is best in attitude
towards his womenfolk.” 

Narrated by al-Tirmidhi (1162); he said it is a hasan saheeh
hadeeth. It was classed as saheeh by al-Albani in Saheeh al-Tirmidhi.
Please see also the answer to question no. 43123. 

And Allah knows best.