Yes. The Quran sets a severe punishment for those who accuse chaste people without four witnesses (24:4), and curses those who slander believing women who never thought of evil (24:23). It is a major sin.
A quienes difamen a las mujeres honestas sin poder presentar cuatro testigos, flageladles con ochenta azotes y nunca más aceptéis su testimonio. Ésos son los perversos.
Malditos sean en la vida de acá y en la otra quienes difamen a las mujeres honestas, incautas pero creyentes. Tendrán un castigo terrible
This is general information, not a fatwa. For your own situation, ask a qualified scholar.
Questions about halal and haram
Is falsely accusing someone of immorality haram?
Yes. The Quran sets a severe punishment for those who accuse chaste people without four witnesses (24:4), and curses those who slander believing women who never thought of evil (24:23). It is a major sin.