Most Rishonim hold that the obligation to love a fellow Jew does not demand a person to feel a specific emotion. Rather, it asks of a Jew specific actions. A Jew must act towards his fellow with care, protecting his property and his honor.
Notably, the Ibn Ezra holds the mitzvah to be literal.
Sources are provided below:
The Rambam writes: Mishneh Torah, Hilchot De’ot 6:4
One must speak praise of another person and be cautious with another’s property in the same way that he desires to be honored and is cautious with his own property.
The Chinuch, Mitzvah 243, writes:
One should treat another person in the way he would treat himself, e.g. protecting his property, preventing him from being harmed, speaking only well of him, respecting him, and certainly not glorifying oneself at his expense...In general, he should act in a way of friendship and love, seeking their benefit and being happy in their good.
The Maharsha writes (Chiddushei Aggadot, Shabbat 31a ):
The answer is that the mitzvah itself is a type of prohibition just like the other mitzvot in this verse, e.g. not taking revenge and not bearing a grudge. “And you shall love your fellow as you love yourself” is not an imperative to bestow an equal amount of goodness upon another, which we know from the legal principle of “Chayecha kodmin” – “Your life comes first.”
However, the Ibn Ezra does write Vayikra 19:18:
In my opinion, the meaning of the verse is as it sounds, namely, that one should love his friend in the same way as himself.
The other commentators disagree with him, but his point still leaves something to strive for.
English translation taken from here.