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.
كسانى كه بر آنان پاكدامن و بىخبر از فحشا و مؤمن تهمت زنا مىزنند، در دنيا و آخرت لعنت شدهاند و برايشان عذابى است بزرگ،
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.