Is the questioner obligated to divorce his wife who committed adultery with her brother before marriage, knowing that she claims she was raped by him, and he seeks stability and fears discord, so should he divorce her or forgive her?

If the wife has repented and no suspicion is evident on her, then she should be kept and not divorced, because repentance erases what came before it. However, if suspicion becomes evident from her, then one should not remain with her in that state. Divorce in such a case would be recommended, or it might even be obligatory. The husband must uphold his right of qawamah (guardianship) over his wife, preventing her from suspicious seclusion and mixing, obliging her to dress modestly and with propriety, teaching her matters of her religion, and having a good opinion of her.