In Kiddushin 41a we read that if the wife is/becomes repulsive to her husband he [might be] overriding/transgressing the Mitzvah of ואהבת:
"דאמר רב יהודה אמר רב אסור לאדם שיקדש את האשה עד שיראנה
שמא יראה בה דבר מגונה ותתגנה עליו
ורחמנא אמר "ואהבת לרעך כמוך"Rav Yehuda says that Rav says: It is forbidden for a man to betroth a woman until he sees her, lest he see something repulsive in her after the betrothal, and she will become repugnant to him, which will cause him to hate her. And the Merciful One states in the Torah: “And you shall love your neighbor as yourself”
Rambam Ishus 3,19: "עַד שֶׁיִּרְאֶנָּה וְתִהְיֶה כְּשֵׁרָה בְּעֵינָיו" seemingly did not have the addition of "ורחמנא אמר" and didn't bring it to Halachah. On the other hand he wrote (Ishus 15):
"וְכֵן צִוּוּ חֲכָמִים שֶׁיִּהְיֶה אָדָם מְכַבֵּד אֶת אִשְׁתּוֹ יוֹתֵר מִגּוּפוֹ וְאוֹהֲבָהּ כְּגוּפוֹ."
But this is learned from the Gemmorah in Yevumos 62b:
"תנו רבנן האוהב את אשתו כגופו והמכבדה יותר מגופו עליו הכתוב אומר וידעת כי שלום אהלך ופקדת נוך ולא תחטא:"
The questions:
What Rabbis learn that the Mitzvah of ואהבת applies to one's wife, based on that Gemmorah in Kiddushin?
Did Rabbis set additional precautions/rulings for a man toward his wife while already married, in order to prevent him from overriding ואהבת?