Let us start with a pasuk in Shir Hashirim, 5:2:
|ב אֲנִי יְשֵׁנָה, וְלִבִּי עֵר; קוֹל דּוֹדִי דוֹפֵק, פִּתְחִי-לִי אֲחֹתִי רַעְיָתִי יוֹנָתִי תַמָּתִי--שֶׁרֹּאשִׁי נִמְלָא-טָל, קְוֻצּוֹתַי רְסִיסֵי לָיְלָה.||2 I sleep, but my heart waketh; Hark! my beloved knocketh: 'Open to me, my sister, my love, my dove, my undefiled; for my head is filled with dew, my locks with the drops of the night.'|
We see that in Biblical Hebrew, ra'yati can mean beloved, not just merely a friend. Chazal make a wonderful derasha in two places on the pasuk of veahavta lerei'acha kamocha, which appears in Vayikra 19:18.
|יח לֹא-תִקֹּם וְלֹא-תִטֹּר אֶת-בְּנֵי עַמֶּךָ, וְאָהַבְתָּ לְרֵעֲךָ כָּמוֹךָ: אֲנִי, ה.||18 Thou shalt not take vengeance, nor bear any grudge against the children of thy people, but thou shalt love thy neighbour as thyself: I am the LORD.|
On a peshat level it means your neighbor, your fellow man. But Chazal darshen the word lerei'acha to mean 'your beloved', as in Shir Hashirim. 'You should love your beloved as yourself.' If they do so, it is not a simple application of the peshat version of the pasuk, but is rather a specialized derasha, on the midrashic level. And then 'love' can plausibly also take a slightly different meaning than it does on a peshat level.
Daat Torah does not realize this and so, in reply to this comment:
DT: "Where does it say that there is a command to love one's wife?"He replies:
Have you excluded "ואהבת לריעך כמוך"?
if you want to go that route then there is nothing unique about the emotional connection between husband and wife - she is no worse then Joe the barber or any strangers one meets during the day. The Rambam is clearly basing himself on the gemora in Yevamos - as all commentaries acknowledge.He asserts that if one gets it from וְאָהַבְתָּ לְרֵעֲךָ כָּמוֹךָ, then there is no distinction from Joe the barber. But this assertion ignores the distinction between peshat in a pasuk and Chazal's derash of a pasuk.
Rav Zilberstein does raise this question - the answer is not very satisfying - but I'll get to the translation soon.
Where is the source for the imperative - the gemora does not say or imply that there is?
Bottom line - according to your approach we need to translate the word ahava - not as love but rather "being concerned for another's welfare."
Here is the contradiction he discusses in the main body of the post:
In the discussion about the nature of marriage - the prime question is the role or necessity for love between husband and wife. It is important to note there is an apparent contradiction between the language of the Talmud and the language of the Rambam and subsequent authorities. The Rambam clearly states that the obligation to love one's wife as oneself is rabbinic. However if he is basing himself on Yevamos (62b) - which the commentaries state is his source - there is no assertion of a rabbinic obligation. It simply says that if one does love one's wife as oneself and a bunch of other things - there will be peace in his tent. At most it is a wise suggestion. An additional problem is that the Rambam in his commentary to the Mishna (Kiddushin 2:1) clearly states that the obligation is from the Torah command to love your fellow as yourself. That is the language of the gemora Kiddushin 41a. So is the Rambam basing his obligation of love on a Torah command or rabbinic? Is he basing himself on Yevamos 62b or Kiddushin 41a? Are there two obligations of love as Rav Zilberberg suggests below? Finally it seems from the following sources that love is refering to caring or not hating or not doing negative things to another person . It is not referring to the emotion that we call love.Yevamos (62b): Our Rabbis taught: If a man loves his wife as himself and honors her more than himself and guides his sons and daughters on the straight path and has them married close to the age of puberty - the verse (Job 5:24) is applied to him, And you shall know that your tent is in peace.Rambam(Hilchos Ishus 3:19): Similarly a man should not marry of a child nor should he marry a woman until he has seen her and she is acceptable in his eyes. That is because if he doesn’t see her first it might turn out that she doesn’t find favor in his eyes when he does see her.Kiddushin (41a): Rav said that it is prohibited for a man to marry a woman until he has seen her because when he does see her he might notice something which disgusts him and the Torah (Vayikra 19:18) has commanded, “You shall love your fellow as yourself.”Rambam (Hilchos Ishus 15:19): Our Sages have commanded that a man should honor his wife more then himself and love her as himself.Rambam(Commentary Kiddushin 2:1): It is correct that each man marry directly rather than through an agent, since we have a general rule that a man should not marry a woman until he has seen her. That is because we are concerned that she won’t find favor in his eyes and yet he will remain married to her in spite of not loving her. Such a thing is prohibited since there is a rule, “You should love your fellow as yourself.” Therefore it is important that the man marries directly rather than through an agent.
It certainly does seem correct that the yellow Rambam passage is based primarily on the yellow gemara and the green Rambam passage is based primarily on the green gemara.
The green passages reflect the explicit derasha, by Rav, of וְאָהַבְתָּ לְרֵעֲךָ כָּמוֹךָ. It is possible that Rambam would consider this to be a rabbinic command rather than a Biblical command, since it is a derasha made on a pasuk, rather than the peshat meaning of the pasuk itself. So even though the Rambam attributes it to וְאָהַבְתָּ לְרֵעֲךָ כָּמוֹךָ, that does not necessitate that this is Biblical, in contradistinction to his statement in Hilchos Ishus that "our Sages have commanded". The green passages, which deal with being married to a person despite not loving them, can carry the connotation of romantic love.
The yellow passages might implicitly reflect the same derasha. This is a brayta, which is Tannaitic, rather than a statement by Rav, an Amora. Yet it states 'if a man loves his wife as himself'. The choice of language clearly reflects the pasuk of וְאָהַבְתָּ לְרֵעֲךָ כָּמוֹךָ. This may or many not refer to romantic love, but it is a reading off of the pasuk.
Why would Rambam summarize the yellow gemara as "our Sages commanded" rather than "the Torah commanded"? Because this is a derasha based on a pasuk, rather than the peshat meaning of the pasuk itself. Or alternatively, because of the continuation of the statement in both the gemara and Rambam, "honors her more than himself", which is a rabbinic extension.
Why would Rambam summarize the yellow gemara as "our Sages commanded" rather than "our Sages recommended"? Because the recommendation (with positive results) is based on a derasha of a pasuk, so clearly Chazal themselves regarded it as an obligation. Indeed, we could turn to Rav's statement in Kiddushin to reveal how Chazal midrashically interpreted the pasuk, and then apply that knowledge to the brayta in Yevamot. Or alternatively, just because Chazal mentioned a positive result of following their directives does not mean that they considered (or Rambam considered) their statement to be only a wise recommendation.