In The Idiot, the love that is possible between two people is compared to the kind of love Christianity urges its followers to feel for all human beings everywhere. For most of the characters, the individualized, personal, sexual, and romantic love seems the most normal, and the most conducive to explaining human behavior. The only person who experiences love differently and is mostly driven by compassionate love for others is Myshkin. His attempt to combine the two into one relationship fails spectacularly.
The only example of romantic "true love" in the novel is Aglaya's marriage to the fake Polish count.
Myshkin's insistence on foisting his compassionate love on women who are sexually impure (Marie, Nastasya) is kind of a reversal of the lies that got these women into their situation in the first place. Originally, they were promised love, but got only sex. Now they are being promised love, but get only dehumanizing pity.